Pyodide support

[anthrotype]

• Detect Emscripten cross-compilation in setup.py, skipping platform-specific sources (CoreText, DirectWrite, Uniscribe)
• Add build-pyodide job to CI workflow
• Upload Pyodide wheel to GitHub releases only (PyPI doesn't accept wasm32 wheels yet, see Add support for wasm32 platform pypi/warehouse#10416 and https://discuss.python.org/t/pep-783-emscripten-packaging)
• Also add tox -e pyodide for local build and test

Fixes #270

[behdad]

I think harfbuzz.cc has all these files automatically included.

[anthrotype]

but harfbuzz.cc lacks the subset module..

[behdad]

Right. That's annoying.

[anthrotype]

@Vipitis the CI finally built some pyodide wheels for uharfbuzz here: https://github.com/harfbuzz/uharfbuzz/actions/runs/20712353445/artifacts/5023130791

Would you like to give them a go? The uharfuzz own tests do pass when run inside a pyodide venv, like cibuildwheel does.

[Vipitis]

hey @anthrotype thanks a lot for figuring this out.

I obtained the wheel yesterday already from your branch and now also from the ci artifacts. The latter has the wrong version number (0.1) which could be a problem for others.
Both wheels work, but I can't test much functionality at the moment since I found additional hurdles apart from uharfbuzz that I will need to look into before our examples run in the browser.

[anthrotype]

thanks for checking. the version number is expected, only when we push a tagged commit to do an actual release we do a full clone and "unshallow" the repository so the correnct version string is obtained from git. The 0.1 is setuptools-scm failing to get a proper tag.