[3.13] gh-112136: Restore removed _PyArg_Parser (GH-121262) (#121344)

gh-112136: Restore removed _PyArg_Parser (GH-121262)

Restore the private _PyArg_Parser structure and the private
_PyArg_ParseTupleAndKeywordsFast() function, previously removed
in Python 3.13 alpha 1.

Recreate Include/cpython/modsupport.h header file.
(cherry picked from commit f8373db153920b890c2e2dd8def249e8df63bcc6)

Co-authored-by: Victor Stinner <vstinner@python.org>