[3.11] pythongh-104372: Cleanup _posixsubprocess make_inheritable f…

…or async signal safety and no GIL requirement (pythonGH-104518)

Move all of the Python C API calls into the parent process up front
instead of doing PyLong_AsLong and PyErr_Occurred and PyTuple_GET from
the post-fork/vfork child process.

Much of this was long overdue. We shouldn't have been using PyTuple and
PyLong APIs within all of these low level functions anyways..
(cherry picked from commit c649df6)

Co-authored-by: Gregory P. Smith <greg@krypto.org>