bpo-35381 Remove all static state from posixmodule (GH-15892)

After #9665, this moves the remaining types in posixmodule to be heap-allocated to make it compatible with PEP384 as well as modifying all the type accessors to fully make the type opaque.

The original PR that got messed up a rebase: https://github.com/python/cpython/pull/10854. All the issues in that commit have now been addressed since https://github.com/python/cpython/pull/11661 got committed.

This change also removes any state from the data segment and onto the module state itself.


https://bugs.python.org/issue35381



Automerge-Triggered-By: @encukou