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.
This comes from #541. We let it as is in case it helps building on Mac.

diff --git a/setupext.py b/setupext.py
--- a/setupext.py
+++ b/setupext.py
@@ -665,6 +665,7 @@ class BackendMacOSX(OptionalPackage):
     name = 'macosx'
 
     def check(self):
+        raise Skipped("MacOSX backend disabled")
         if sys.platform != 'darwin':
             raise Skipped("Mac OS-X only")
         return super().check()
-- 
2.20.1

This comes from #541. We let it as is in case it helps building on Mac.

diff --git a/setupext.py b/setupext.py
--- a/setupext.py
+++ b/setupext.py
@@ -665,6 +665,7 @@ class BackendMacOSX(OptionalPackage):
     name = 'macosx'
 
     def check(self):
+        raise Skipped("MacOSX backend disabled")
         if sys.platform != 'darwin':
             raise Skipped("Mac OS-X only")
         return super().check()
-- 
2.20.1
