Begin converting away from pkg_resources

[matteius]

Starts fixing #5349

The issue

• Cleanup some patching to be consistent with how we patch pipenv to be available internal to pip __main__.py which is a more modern way using importlib that does not rely on pkg_resoruces.

There is more work to do to fully drop pkg_resources which seems to be what we are supposed to do: https://setuptools.pypa.io/en/latest/pkg_resources.html

The problem enters with pipdeptree is expecting the pkg_resources Distribution. I opened tox-dev/pipdeptree#175 to have that discussion.

[matteius]

Ok, figured out my blockers with the prior PR, and so closing this in favor of: #5350
which will depend on: sarugaku/requirementslib#343