gh-85283: Add PyMem_RawMalloc() to the limited C API (#108570)

Add PyMem_RawMalloc(), PyMem_RawCalloc(), PyMem_RawRealloc() and
PyMem_RawFree() to the limited C API.

These functions were added by Python 3.4 and are needed to port
stdlib extensions to the limited C API, like grp and pwd.

Co-authored-by: Erlend E. Aasland <erlend@python.org>