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: packaging
  version: '20.9'
source:
  sha256: 5b327ac1320dc863dca72f4514ecc086f31186744b84a230374cc1fd776feae5
  url: https://files.pythonhosted.org/packages/86/3c/bcd09ec5df7123abcf695009221a52f90438d877a2f1499453c6938f5728/packaging-20.9.tar.gz

requirements:
  run:
  - pyparsing

test:
  imports:
  - packaging

package:
  name: packaging
  version: '20.9'
source:
  sha256: 5b327ac1320dc863dca72f4514ecc086f31186744b84a230374cc1fd776feae5
  url: https://files.pythonhosted.org/packages/86/3c/bcd09ec5df7123abcf695009221a52f90438d877a2f1499453c6938f5728/packaging-20.9.tar.gz

requirements:
  run:
  - pyparsing

test:
  imports:
  - packaging
