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- [x] Add new / update outdated documentation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)

from functools import update_wrapper
from textwrap import dedent
from typing import Any


def delete_attrs(cls):
    """Prevent attributes of a class or module from being documented.

    The top level documentation comment of the class or module will still be
    rendered.
    """
    for name in dir(cls):
        if not name.startswith("_"):
            try:
                delattr(cls, name)
            except Exception:
                pass


def docs_argspec(argspec: str) -> Any:
    """Decorator to override the argument spec of the function that is
    rendered in the docs.

    If the documentation finds a __wrapped__ attribute, it will use that to
    render the argspec instead of the function itself. Assign an appropriate
    fake function to __wrapped__ with the desired argspec.
    """

    def dec(func):
        d = func.__globals__
        TEMP_NAME = "_xxxffff___"
        assert TEMP_NAME not in d
        code = dedent(
            f"""\
            def {TEMP_NAME}{argspec}:
                pass
            """
        )
        # exec in func.__globals__ context so that type hints don't case NameErrors.
        exec(code, d)
        f = d.pop(TEMP_NAME)

        # # Run update_wrapper but keep f's annotations and don't set
        # # f.__wrapped__ (would cause an infinite loop!)
        annotations = f.__annotations__
        update_wrapper(f, func)
        f.__annotations__ = annotations
        del f.__wrapped__

        # Set wrapper to be our fake function
        func.__wrapped__ = f

        return func

    return dec

from functools import update_wrapper
from textwrap import dedent
from typing import Any


def delete_attrs(cls):
    """Prevent attributes of a class or module from being documented.

    The top level documentation comment of the class or module will still be
    rendered.
    """
    for name in dir(cls):
        if not name.startswith("_"):
            try:
                delattr(cls, name)
            except Exception:
                pass


def docs_argspec(argspec: str) -> Any:
    """Decorator to override the argument spec of the function that is
    rendered in the docs.

    If the documentation finds a __wrapped__ attribute, it will use that to
    render the argspec instead of the function itself. Assign an appropriate
    fake function to __wrapped__ with the desired argspec.
    """

    def dec(func):
        d = func.__globals__
        TEMP_NAME = "_xxxffff___"
        assert TEMP_NAME not in d
        code = dedent(
            f"""\
            def {TEMP_NAME}{argspec}:
                pass
            """
        )
        # exec in func.__globals__ context so that type hints don't case NameErrors.
        exec(code, d)
        f = d.pop(TEMP_NAME)

        # # Run update_wrapper but keep f's annotations and don't set
        # # f.__wrapped__ (would cause an infinite loop!)
        annotations = f.__annotations__
        update_wrapper(f, func)
        f.__annotations__ = annotations
        del f.__wrapped__

        # Set wrapper to be our fake function
        func.__wrapped__ = f

        return func

    return dec
