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: distlib
  version: 0.3.1
source:
  sha256: edf6116872c863e1aa9d5bb7cb5e05a022c519a4594dc703843343a9ddd9bff1
  url: https://files.pythonhosted.org/packages/2f/83/1eba07997b8ba58d92b3e51445d5bf36f9fba9cb8166bcae99b9c3464841/distlib-0.3.1.zip
build:
  script: "find . -name *.exe -delete"
test:
  imports:
  - distlib

package:
  name: distlib
  version: 0.3.1
source:
  sha256: edf6116872c863e1aa9d5bb7cb5e05a022c519a4594dc703843343a9ddd9bff1
  url: https://files.pythonhosted.org/packages/2f/83/1eba07997b8ba58d92b3e51445d5bf36f9fba9cb8166bcae99b9c3464841/distlib-0.3.1.zip
build:
  script: "find . -name *.exe -delete"
test:
  imports:
  - distlib
