Add official PyEmscripten / WebAssembly wheels to PyPI?

[oakaigh]

Upstream libav/ffmpeg already supports wasm, adding this would allow pyav to be used directly in browser (which opens door to many python-based video editing/viewing applications).
Plus, PEP 783 already standardizes wasm wheels.

Seealso: https://pyodide.org/en/stable/development/building-packages.html

[WyattBlue]

I don't want to build official wasm wheels at all, let alone put them on PyPI. First reason is that PyEmscripten doesn't appear to support the threading module. Second is that emscripten appears to treat dynamic linking as experimental and would lead to a lot of churn.