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- [x] Add new / update outdated documentation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)

(python-api)=

# Python API

Backward compatibility of the API is not guaranteed at this point.

**JavaScript Modules**

By default there are two JavaScript modules. More can be added with
{js:func}`pyodide.registerJsModule`. You can import these modules using the Python
`import` statement in the normal way.

```{eval-rst}
.. list-table::

   *  - ``js``
      - The global JavaScript scope.
   *  - :js:mod:`pyodide_js <pyodide>`
      - The JavaScript Pyodide module.
```

**Python Modules**

```{eval-rst}
.. list-table::

   *  - :py:mod:`pyodide.code`
      - Utilities for evaluating Python and JavaScript code.
   *  - :py:mod:`pyodide.console`
      - Similar to the Python builtin `code` module but handles top level await. Used
        for implementing the Pyodide console.
   *  - :py:mod:`pyodide.ffi`
      - The :py:class:`~pyodide.ffi.JsProxy` class and utilities to help interact with JavaScript code.
   *  - :py:mod:`pyodide.http`
      - Defines :py:func:`~pyodide.http.pyfetch` and other functions for making network requests.
   *  - :py:mod:`pyodide.webloop`
      - The Pyodide event loop implementation. This is automatically configured
        correctly for most use cases it is unlikely you will need it outside of niche
        use cases.
```

```{eval-rst}
.. toctree::
   :hidden:

   python-api/code.md
   python-api/console.md
   python-api/ffi.md
   python-api/http.md
   python-api/webloop.md
```

(python-api)=

# Python API

Backward compatibility of the API is not guaranteed at this point.

**JavaScript Modules**

By default there are two JavaScript modules. More can be added with
{js:func}`pyodide.registerJsModule`. You can import these modules using the Python
`import` statement in the normal way.

```{eval-rst}
.. list-table::

   *  - ``js``
      - The global JavaScript scope.
   *  - :js:mod:`pyodide_js <pyodide>`
      - The JavaScript Pyodide module.
```

**Python Modules**

```{eval-rst}
.. list-table::

   *  - :py:mod:`pyodide.code`
      - Utilities for evaluating Python and JavaScript code.
   *  - :py:mod:`pyodide.console`
      - Similar to the Python builtin `code` module but handles top level await. Used
        for implementing the Pyodide console.
   *  - :py:mod:`pyodide.ffi`
      - The :py:class:`~pyodide.ffi.JsProxy` class and utilities to help interact with JavaScript code.
   *  - :py:mod:`pyodide.http`
      - Defines :py:func:`~pyodide.http.pyfetch` and other functions for making network requests.
   *  - :py:mod:`pyodide.webloop`
      - The Pyodide event loop implementation. This is automatically configured
        correctly for most use cases it is unlikely you will need it outside of niche
        use cases.
```

```{eval-rst}
.. toctree::
   :hidden:

   python-api/code.md
   python-api/console.md
   python-api/ffi.md
   python-api/http.md
   python-api/webloop.md
```
