Packages the distutils stdlib module as a standalone package,
```
377K distutils.data
221K distutils.data.br
19K distutils.js
```
to reduce the minimal pyodide size.

Part of #1542 

This also,
 - adds documentation on what's supported or not in the stdlib
 - makes a few changes to `pyodide_build/buildall.py` to be able to add such stdlib packages as a dependency in other packages (which didn't work before). For instance, until there is a release with https://github.com/pypa/packaging/pull/396 micropip has a dependency on distutils.
Unvendor distutils. Packages the distutils stdlib module as a standalone package,
```
377K distutils.data
221K distutils.data.br
19K distutils.js
```
to reduce the minimal pyodide size.

Part of #1542 

This also,
 - adds documentation on what's supported or not in the stdlib
 - makes a few changes to `pyodide_build/buildall.py` to be able to add such stdlib packages as a dependency in other packages (which didn't work before). For instance, until there is a release with https://github.com/pypa/packaging/pull/396 micropip has a dependency on distutils.
package:
  name: regex
  version: 2021.4.4
source:
  sha256: 52ba3d3f9b942c49d7e4bc105bb28551c44065f139a65062ab7912bef10c9afb
  url: https://files.pythonhosted.org/packages/38/3f/4c42a98c9ad7d08c16e7d23b2194a0e4f3b2914662da8bc88986e4e6de1f/regex-2021.4.4.tar.gz
test:
  imports:
  - regex

package:
  name: regex
  version: 2021.4.4
source:
  sha256: 52ba3d3f9b942c49d7e4bc105bb28551c44065f139a65062ab7912bef10c9afb
  url: https://files.pythonhosted.org/packages/38/3f/4c42a98c9ad7d08c16e7d23b2194a0e4f3b2914662da8bc88986e4e6de1f/regex-2021.4.4.tar.gz
test:
  imports:
  - regex
