This adds a step that generates an xbuildenv to the circleci CI and
deploys it to github releases when we make a release. I also updated
the url in download_xbuildenv to point to github releases.
We are pushing pyodide_build to PyPI as a Python package, but for now,
installing pyodide_build from PyPI (i.e. pip install pyodide_build`) is almost
useless because:
there are bunch of hard-coded paths (e.g. Path(__file__).parents[2]),
its dependencies are not specified in setup.cfg.
This PR is for mitigating this situation by removing hard-coded paths and
adding tests, and is also a preparation for our new CLI
(https://github.com/pyodide/pyodide/issues/1977).
Fixing a minor issue - pyodide-build doesn't work out of the box, it's missing two requirements.
Also updating a typo in the docs, and minor pre-commit bump.