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: Jinja2
  version: 2.11.3
requirements:
  run:
  - MarkupSafe
source:
  sha256: a6d58433de0ae800347cab1fa3043cebbabe8baa9d29e668f1c768cb87a333c6
  url: https://files.pythonhosted.org/packages/4f/e7/65300e6b32e69768ded990494809106f87da1d436418d5f1367ed3966fd7/Jinja2-2.11.3.tar.gz
test:
  imports:
  - jinja2

package:
  name: Jinja2
  version: 2.11.3
requirements:
  run:
  - MarkupSafe
source:
  sha256: a6d58433de0ae800347cab1fa3043cebbabe8baa9d29e668f1c768cb87a333c6
  url: https://files.pythonhosted.org/packages/4f/e7/65300e6b32e69768ded990494809106f87da1d436418d5f1367ed3966fd7/Jinja2-2.11.3.tar.gz
test:
  imports:
  - jinja2
