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: traits
  version: 6.2.0
source:
  sha256: 16fa1518b0778fd53bf0547e6a562b1787bf68c8f6b7995a13bd1902529fdb0c
  url: https://files.pythonhosted.org/packages/44/f3/2fd5d25717536009cbc967449b5598fab7fe9466b84a758fc2f83ebd2c7e/traits-6.2.0.tar.gz
test:
  imports:
  - traits

package:
  name: traits
  version: 6.2.0
source:
  sha256: 16fa1518b0778fd53bf0547e6a562b1787bf68c8f6b7995a13bd1902529fdb0c
  url: https://files.pythonhosted.org/packages/44/f3/2fd5d25717536009cbc967449b5598fab7fe9466b84a758fc2f83ebd2c7e/traits-6.2.0.tar.gz
test:
  imports:
  - traits
