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: bleach
  version: 3.3.0
requirements:
  run:
  - webencodings
  - packaging
  - six
source:
  sha256: 98b3170739e5e83dd9dc19633f074727ad848cbedb6026708c8ac2d3b697a433
  url: https://files.pythonhosted.org/packages/70/84/2783f734240fab7815a00b419c4281d2d0984971de30b08176aae2acff10/bleach-3.3.0.tar.gz
test:
  imports:
  - bleach

package:
  name: bleach
  version: 3.3.0
requirements:
  run:
  - webencodings
  - packaging
  - six
source:
  sha256: 98b3170739e5e83dd9dc19633f074727ad848cbedb6026708c8ac2d3b697a433
  url: https://files.pythonhosted.org/packages/70/84/2783f734240fab7815a00b419c4281d2d0984971de30b08176aae2acff10/bleach-3.3.0.tar.gz
test:
  imports:
  - bleach
