Mark distutils as py.typed

[Avasam]

I thought this wouldn't do anything shipped as a setuptools submodule, but it turns out pyright does understand it as part of its support for submodules for namespace packages. So it's actually useful.

The spec isn't completely clear here. But for type-checkers that understand it: it's a benefit. And for those that don't, nothing changes.

I think distutils/compilers is considered a namespace package, hence the need for the second py.typed

Without:

With:

Relates to:

• Experiment: removing setuptools._distutils python/typeshed#13627
• [FR] Vendor distutils stubs setuptools#4689
  • Statically alias distutils-stubs to setuptools._distutils setuptools#4704
  • [Waiting for distutils sync] Generate distutils-stubs on install setuptools#4861

[Avasam]

@jaraco By all means this shouldn't affect users in any way, but should help me with a WIP PR in setuptools and in typeshed.