Exclude top-level .tox|.nox|.venv from sdist

[abravalheri]

Summary of changes

This is a follow up on #4602: instead of doing an ad-hoc exclusion rule for setuptools' own MANIFEST.in, this PR proposes to always "prune" the .tox, .nox and .venv top-level directories.

This is done by extending the sdist.prune_file_list method from distutils using the same technique that the original method already uses to exclude directories like .git or .svn.

I am only excluding top-level .tox|.nox|.venv directories to be conservative and minimise Hyrum's law unexpected consequences.

This PR also removes the custom implementation on setuptools.command.egg_info:manifest_maker.prune_file_list and instead let the class just access the parent's class implementation via inheritance:

• By comparing the removed lines with the distutils' implementation, I can see that manifest_maker is basically re-implementing the functionality.
• I double checked that the implementation is present in CPython 3.8, so SETUPTOOLS_USE_DISTUTILS=stdlib should not affect this particular aspect.

Finally, it is important to notice that once the implementation of sdist prunes these directories, the user cannot add them back via MANIFEST.in. But I think that is OK.

I did a quick search on Github, and it seems that most of the users are trying to exclude the directories (on a quick/not-thorough inspection I did not see anyone intentionally including them).

Closes #4601

Pull Request Checklist

• Changes have tests
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