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: scikit-image
  version: 0.15.0
source:
  patches:
  - patches/no-openmp.patch
  - patches/unwrap.patch
  - patches/preferred_plugins.patch
  sha256: df111e654b47e5ea456c50553debe4c5ddd97258894c7ad3b7f2f9f10798e053
  url: https://files.pythonhosted.org/packages/e0/46/ca035f5d7d3414124a3a5ef22cd2e75c0c5149042a668375f1d44eb69f8f/scikit-image-0.15.0.tar.gz
requirements:
  run:
    - numpy
    - scipy
    - matplotlib
    - networkx
    - pillow
    - imageio
    - pywavelets
test:
  imports:
  - skimage

package:
  name: scikit-image
  version: 0.15.0
source:
  patches:
  - patches/no-openmp.patch
  - patches/unwrap.patch
  - patches/preferred_plugins.patch
  sha256: df111e654b47e5ea456c50553debe4c5ddd97258894c7ad3b7f2f9f10798e053
  url: https://files.pythonhosted.org/packages/e0/46/ca035f5d7d3414124a3a5ef22cd2e75c0c5149042a668375f1d44eb69f8f/scikit-image-0.15.0.tar.gz
requirements:
  run:
    - distutils
    - numpy
    - scipy
    - matplotlib
    - networkx
    - pillow
    - imageio
    - pywavelets
test:
  imports:
  - skimage
