ENH Support SDL-based packages and add pyxel. ### Description

This adds SDL-based package support to Pyodide and adds pyxel as a PoC. Most of the troubleshooting is done by @kitao and pyxel devs, a big thanks to them.

This is on top of #3505

1) I linked only js part of SDL libraries to the main module and linked the native parts to the side module. So the size increase of the main module is small enough (~0.1MB increase to the pyodide.asm.js).

Before (in #3505):

```
5145705 pyodide.asm.data
1204075 pyodide.asm.js
8862216 pyodide.asm.wasm
```

After:

```
5145705 pyodide.asm.data
1346524 pyodide.asm.js
8905514 pyodide.asm.wasm
```

2) Emscripten draws everything into `Module.canvas`, but the canvas attribute is not set automatically (which makes sense as we don't output any HTML), so it is the user's job to set it manually.

For now, I am thinking of just mentioning it in the FAQ entry, "you need to set pyodide._module.canvas = ...". But it would be probably nice to have an API to set canvas, as pyodide._module is a private attribute.

### Checklists

- [x] Add a [CHANGELOG](https://github.com/pyodide/pyodide/blob/main/docs/project/changelog.md) entry
- [x] Add / update tests
- [x] Add new / update outdated documentation

### Demo

https://ryanking13.github.io/pyodide-pyxel-test

(mostly borrowed from the pyxel repository: https://github.com/kitao/pyxel/tree/main/wasm)

import os
import re
import shutil
import tempfile
from pathlib import Path
from typing import Optional
from urllib.parse import urlparse

import requests
import typer

from .. import common
from ..out_of_tree import build
from ..out_of_tree.pypi import (
    build_dependencies_for_wheel,
    build_wheels_from_pypi_requirements,
    fetch_pypi_package,
)
from ..out_of_tree.utils import initialize_pyodide_root


def pypi(
    package: str,
    exports: str = typer.Option(
        "requested",
        help="Which symbols should be exported when linking .so files?",
    ),
    ctx: typer.Context = typer.Context,
) -> Path:
    """Fetch a wheel from pypi, or build from source if none available."""
    initialize_pyodide_root()
    common.check_emscripten_version()
    backend_flags = ctx.args
    curdir = Path.cwd()
    (curdir / "dist").mkdir(exist_ok=True)

    with tempfile.TemporaryDirectory() as tmpdir:
        temppath = Path(tmpdir)

        # get package from pypi
        package_path = fetch_pypi_package(package, temppath)
        if not package_path.is_dir():
            # a pure-python wheel has been downloaded - just copy to dist folder
            dest_file = curdir / "dist" / package_path.name
            shutil.copyfile(str(package_path), curdir / "dist" / package_path.name)
            print(f"Successfully fetched: {package_path.name}")
            return dest_file

        # sdist - needs building
        os.chdir(tmpdir)
        built_wheel = build.run(exports, backend_flags, outdir=curdir / "dist")
        os.chdir(curdir)
        return built_wheel


def url(
    package_url: str,
    exports: str = typer.Option(
        "requested",
        help="Which symbols should be exported when linking .so files?",
    ),
    ctx: typer.Context = typer.Context,
) -> Path:
    """Fetch a wheel or build sdist from url."""
    initialize_pyodide_root()
    common.check_emscripten_version()
    backend_flags = ctx.args
    curdir = Path.cwd()
    (curdir / "dist").mkdir(exist_ok=True)
    with requests.get(package_url, stream=True) as response:
        parsed_url = urlparse(response.url)
        filename = os.path.basename(parsed_url.path)
        name_base, ext = os.path.splitext(filename)
        if ext == ".gz" and name_base.rfind(".") != -1:
            ext = name_base[name_base.rfind(".") :] + ext
        if ext.lower() == ".whl":
            # just copy wheel into dist and return
            out_path = Path(f"dist/{filename}").resolve()
            with open(out_path, "b") as f:
                for chunk in response.iter_content(chunk_size=1048576):
                    f.write(chunk)
            return out_path
        else:
            tf = tempfile.NamedTemporaryFile(suffix=ext, delete=False)
            for chunk in response.iter_content(chunk_size=1048576):
                tf.write(chunk)
            tf.close()
            with tempfile.TemporaryDirectory() as tmpdir:
                temppath = Path(tmpdir)
                shutil.unpack_archive(tf.name, tmpdir)
                folder_list = list(temppath.iterdir())
                if len(folder_list) == 1 and folder_list[0].is_dir():
                    # unzipped into subfolder
                    os.chdir(folder_list[0])
                else:
                    # unzipped here
                    os.chdir(temppath)
                wheel_path = build.run(exports, backend_flags, outdir=curdir / "dist")
            os.unlink(tf.name)
            return wheel_path


def source(
    source_location: str,
    exports: str = typer.Option(
        "requested",
        help="Which symbols should be exported when linking .so files?",
    ),
    ctx: typer.Context = typer.Context,
) -> Path:
    """Use pypa/build to build a Python package from source"""
    initialize_pyodide_root()
    orig_dir = Path.cwd()
    if source_location != ".":
        # build in this folder
        os.chdir(source_location)
    common.check_emscripten_version()
    backend_flags = ctx.args
    built_wheel = build.run(exports, backend_flags, outdir=orig_dir / "dist")
    os.chdir(orig_dir)
    return built_wheel


# simple 'pyodide build' command
def main(
    source_location: "Optional[str]" = typer.Argument(
        "",
        help="Build source, can be source folder, pypi version specification, or url to a source dist archive or wheel file. If this is blank, it will build the current directory.",
    ),
    requirements_txt: str = typer.Option(
        "",
        "--requirements",
        "-r",
        help="Build a list of package requirements from a requirements.txt file",
    ),
    exports: str = typer.Option(
        "requested",
        help="Which symbols should be exported when linking .so files?",
    ),
    build_dependencies: bool = typer.Option(
        False, help="Fetch non-pyodide dependencies from pypi and build them too."
    ),
    output_lockfile: str = typer.Option(
        "",
        help="Output list of resolved dependencies to a file in requirements.txt format",
    ),
    skip_dependency: list[str] = typer.Option(
        [],
        help="Skip building or resolving a single dependency. Use multiple times or provide a comma separated list to skip multiple dependencies.",
    ),
    compression_level: int = typer.Option(
        6, help="Compression level to use for the created zip file"
    ),
    ctx: typer.Context = typer.Context,
) -> None:
    """Use pypa/build to build a Python package from source, pypi or url."""
    extras: list[str] = []

    if len(requirements_txt) > 0:
        # a requirements.txt - build it (and optionally deps)
        if not Path(requirements_txt).exists():
            raise RuntimeError(
                f"Couldn't find requirements text file {requirements_txt}"
            )
        reqs = []
        with open(requirements_txt) as f:
            raw_reqs = [x.strip() for x in f.readlines()]
        for x in raw_reqs:
            # remove comments
            comment_pos = x.find("#")
            if comment_pos != -1:
                x = x[:comment_pos].strip()
            if len(x) > 0:
                if x[0] == "-":
                    raise RuntimeError(
                        f"pyodide build only supports name-based PEP508 requirements. [{x}] will not work."
                    )
                if x.find("@") != -1:
                    raise RuntimeError(
                        f"pyodide build does not support URL based requirements. [{x}] will not work"
                    )
                reqs.append(x)
        try:
            build_wheels_from_pypi_requirements(
                reqs,
                Path("./dist").resolve(),
                build_dependencies,
                skip_dependency,
                exports,
                ctx.args,
                output_lockfile=output_lockfile,
            )
        except BaseException as e:
            import traceback

            print("Failed building multiple wheels:", traceback.format_exc())
            raise e
        return

    if source_location is not None:
        extras = re.findall(r"\[(\w+)\]", source_location)
        if len(extras) != 0:
            source_location = source_location[0 : source_location.find("[")]
    if not source_location:
        # build the current folder
        wheel = source(".", exports, ctx)
    elif source_location.find("://") != -1:
        wheel = url(source_location, exports, ctx)
    elif Path(source_location).is_dir():
        # a folder, build it
        wheel = source(source_location, exports, ctx)
    elif source_location.find("/") == -1:
        # try fetch or build from pypi
        wheel = pypi(source_location, exports, ctx)
    else:
        raise RuntimeError(f"Couldn't determine source type for {source_location}")
    # now build deps for wheel
    if build_dependencies:
        try:
            build_dependencies_for_wheel(
                wheel,
                extras,
                skip_dependency,
                exports,
                ctx.args,
                output_lockfile=output_lockfile,
                compression_level=compression_level,
            )
        except BaseException as e:
            import traceback

            print("Failed building dependencies for wheel:", traceback.format_exc())
            wheel.unlink()
            raise e


main.typer_kwargs = {  # type: ignore[attr-defined]
    "context_settings": {
        "ignore_unknown_options": True,
        "allow_extra_args": True,
    },
}

import os
import re
import shutil
import tempfile
from pathlib import Path
from typing import Optional
from urllib.parse import urlparse

import requests
import typer

from .. import common
from ..out_of_tree import build
from ..out_of_tree.pypi import (
    build_dependencies_for_wheel,
    build_wheels_from_pypi_requirements,
    fetch_pypi_package,
)
from ..out_of_tree.utils import initialize_pyodide_root


def pypi(
    package: str,
    exports: str = typer.Option(
        "requested",
        help="Which symbols should be exported when linking .so files?",
    ),
    ctx: typer.Context = typer.Context,
) -> Path:
    """Fetch a wheel from pypi, or build from source if none available."""
    initialize_pyodide_root()
    common.check_emscripten_version()
    backend_flags = ctx.args
    curdir = Path.cwd()
    (curdir / "dist").mkdir(exist_ok=True)

    with tempfile.TemporaryDirectory() as tmpdir:
        temppath = Path(tmpdir)

        # get package from pypi
        package_path = fetch_pypi_package(package, temppath)
        if not package_path.is_dir():
            # a pure-python wheel has been downloaded - just copy to dist folder
            dest_file = curdir / "dist" / package_path.name
            shutil.copyfile(str(package_path), curdir / "dist" / package_path.name)
            print(f"Successfully fetched: {package_path.name}")
            return dest_file

        # sdist - needs building
        os.chdir(tmpdir)
        built_wheel = build.run(exports, backend_flags, outdir=curdir / "dist")
        os.chdir(curdir)
        return built_wheel


def url(
    package_url: str,
    exports: str = typer.Option(
        "requested",
        help="Which symbols should be exported when linking .so files?",
    ),
    ctx: typer.Context = typer.Context,
) -> Path:
    """Fetch a wheel or build sdist from url."""
    initialize_pyodide_root()
    common.check_emscripten_version()
    backend_flags = ctx.args
    curdir = Path.cwd()
    (curdir / "dist").mkdir(exist_ok=True)
    with requests.get(package_url, stream=True) as response:
        parsed_url = urlparse(response.url)
        filename = os.path.basename(parsed_url.path)
        name_base, ext = os.path.splitext(filename)
        if ext == ".gz" and name_base.rfind(".") != -1:
            ext = name_base[name_base.rfind(".") :] + ext
        if ext.lower() == ".whl":
            # just copy wheel into dist and return
            out_path = Path(f"dist/{filename}").resolve()
            with open(out_path, "b") as f:
                for chunk in response.iter_content(chunk_size=1048576):
                    f.write(chunk)
            return out_path
        else:
            tf = tempfile.NamedTemporaryFile(suffix=ext, delete=False)
            for chunk in response.iter_content(chunk_size=1048576):
                tf.write(chunk)
            tf.close()
            with tempfile.TemporaryDirectory() as tmpdir:
                temppath = Path(tmpdir)
                shutil.unpack_archive(tf.name, tmpdir)
                folder_list = list(temppath.iterdir())
                if len(folder_list) == 1 and folder_list[0].is_dir():
                    # unzipped into subfolder
                    os.chdir(folder_list[0])
                else:
                    # unzipped here
                    os.chdir(temppath)
                wheel_path = build.run(exports, backend_flags, outdir=curdir / "dist")
            os.unlink(tf.name)
            return wheel_path


def source(
    source_location: str,
    exports: str = typer.Option(
        "requested",
        help="Which symbols should be exported when linking .so files?",
    ),
    ctx: typer.Context = typer.Context,
) -> Path:
    """Use pypa/build to build a Python package from source"""
    initialize_pyodide_root()
    orig_dir = Path.cwd()
    if source_location != ".":
        # build in this folder
        os.chdir(source_location)
    common.check_emscripten_version()
    backend_flags = ctx.args
    built_wheel = build.run(exports, backend_flags, outdir=orig_dir / "dist")
    os.chdir(orig_dir)
    return built_wheel


# simple 'pyodide build' command
def main(
    source_location: "Optional[str]" = typer.Argument(
        "",
        help="Build source, can be source folder, pypi version specification, or url to a source dist archive or wheel file. If this is blank, it will build the current directory.",
    ),
    requirements_txt: str = typer.Option(
        "",
        "--requirements",
        "-r",
        help="Build a list of package requirements from a requirements.txt file",
    ),
    exports: str = typer.Option(
        "requested",
        help="Which symbols should be exported when linking .so files?",
    ),
    build_dependencies: bool = typer.Option(
        False, help="Fetch non-pyodide dependencies from pypi and build them too."
    ),
    output_lockfile: str = typer.Option(
        "",
        help="Output list of resolved dependencies to a file in requirements.txt format",
    ),
    skip_dependency: list[str] = typer.Option(
        [],
        help="Skip building or resolving a single dependency. Use multiple times or provide a comma separated list to skip multiple dependencies.",
    ),
    compression_level: int = typer.Option(
        6, help="Compression level to use for the created zip file"
    ),
    ctx: typer.Context = typer.Context,
) -> None:
    """Use pypa/build to build a Python package from source, pypi or url."""
    extras: list[str] = []

    if len(requirements_txt) > 0:
        # a requirements.txt - build it (and optionally deps)
        if not Path(requirements_txt).exists():
            raise RuntimeError(
                f"Couldn't find requirements text file {requirements_txt}"
            )
        reqs = []
        with open(requirements_txt) as f:
            raw_reqs = [x.strip() for x in f.readlines()]
        for x in raw_reqs:
            # remove comments
            comment_pos = x.find("#")
            if comment_pos != -1:
                x = x[:comment_pos].strip()
            if len(x) > 0:
                if x[0] == "-":
                    raise RuntimeError(
                        f"pyodide build only supports name-based PEP508 requirements. [{x}] will not work."
                    )
                if x.find("@") != -1:
                    raise RuntimeError(
                        f"pyodide build does not support URL based requirements. [{x}] will not work"
                    )
                reqs.append(x)
        try:
            build_wheels_from_pypi_requirements(
                reqs,
                Path("./dist").resolve(),
                build_dependencies,
                skip_dependency,
                exports,
                ctx.args,
                output_lockfile=output_lockfile,
            )
        except BaseException as e:
            import traceback

            print("Failed building multiple wheels:", traceback.format_exc())
            raise e
        return

    if source_location is not None:
        extras = re.findall(r"\[(\w+)\]", source_location)
        if len(extras) != 0:
            source_location = source_location[0 : source_location.find("[")]
    if not source_location:
        # build the current folder
        wheel = source(".", exports, ctx)
    elif source_location.find("://") != -1:
        wheel = url(source_location, exports, ctx)
    elif Path(source_location).is_dir():
        # a folder, build it
        wheel = source(source_location, exports, ctx)
    elif source_location.find("/") == -1:
        # try fetch or build from pypi
        wheel = pypi(source_location, exports, ctx)
    else:
        raise RuntimeError(f"Couldn't determine source type for {source_location}")
    # now build deps for wheel
    if build_dependencies:
        try:
            build_dependencies_for_wheel(
                wheel,
                extras,
                skip_dependency,
                exports,
                ctx.args,
                output_lockfile=output_lockfile,
                compression_level=compression_level,
            )
        except BaseException as e:
            import traceback

            print("Failed building dependencies for wheel:", traceback.format_exc())
            wheel.unlink()
            raise e


main.typer_kwargs = {  # type: ignore[attr-defined]
    "context_settings": {
        "ignore_unknown_options": True,
        "allow_extra_args": True,
    },
}
