Miscellaneous updates for Pyodide 0.27: bump WASM CI and revise Arrow compatibility note
- [ ] ~closes #xxxx (Replace xxxx with the GitHub issue number)~
- [x] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [x] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [ ] ~Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.~
- [ ] ~Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.~

I noticed via #60747 that the Pyodide CI job for `pandas` in `unit-tests.yml` is still using a version of Pyodide[^1] that is quite old by this point; we no longer support it, as we have recently released Pyodide 0.27 this January (https://github.com/pyodide/pyodide/releases/tag/0.27.1). On the other hand, `cibuildwheel` in `wheels.yml` builds against Pyodide 0.26 at the moment.

Other notes around the changes here:
- we unvendored `pyodide-build` from the Pyodide runtime/repository, so its version does not stay in sync with the Pyodide runtime version.
- the Node.js version has been bumped to 20, though 22 should work, too.
- the Pyodide cross-build environment folder has been added to the `.gitignore` file
- PyArrow is now [supported](https://github.com/joemarshall/pyarrow-pyodide/) in Pyodide/WASM ([docs on compilation](https://arrow.apache.org/docs/developers/cpp/emscripten.html)), and I've updated the PDEP-10 document here to remove the point surrounding its previous unavailability in Pyodide/PyScript/other WASM environments.
- I removed an expected failure case in `TestCoercionFloat32.test_setitem` that now xpasses with Emscripten 3.1.58.

Please let me know if you want me to split any of the changes to a different PR. Thank you!

[^1]: I have plans in mind to make these upgrades more seamless via https://github.com/pyodide/pyodide-actions/issues/12 by letting Dependabot do such a job, but I haven't got around to sitting down and spending a bit of time doing so.
> On the other hand, cibuildwheel in wheels.yml builds against Pyodide 0.26 at the moment.

Could you bump pyodide in for the wheel builds then to match the version in our unit tests? > > On the other hand, cibuildwheel in wheels.yml builds against Pyodide 0.26 at the moment.
> 
> Could you bump pyodide in for the wheel builds then to match the version in our unit tests?

I could,  but it needs this PR to make it to a release: https://github.com/pypa/cibuildwheel/pull/2117 > I could, but it needs this PR to make it to a release: https://github.com/pypa/cibuildwheel/pull/2117

OK no problem. Thanks @agriyakhetarpal 