Fix Python.h to build C extensions with Xcode: remove a relative
include from Include/cpython/pystate.h.

(cherry picked from commit 4ae26b9c1d0c33e3db92c6f305293f9240dea358)

Automerge-Triggered-By: GH:benjaminp
(cherry picked from commit 196998e220d6ca030e5a1c8ad63fcaed8e049a98)

Co-authored-by: Geoffrey Thomas <geofft@ldpreload.com>

(cherry picked from commit 31aa0dbff4c1d39c9d77c6c8f4a61d0e46c1268b)

Co-authored-by: Mark Shannon <mark@hotpy.org>

Enhance also the documentation of debug hooks on memory allocators.

Remove the pyarena.h header file with functions:

* PyArena_New()
* PyArena_Free()
* PyArena_Malloc()
* PyArena_AddPyObject()

These functions were undocumented, excluded from the limited C API,
and were only used internally by the compiler.

Add pycore_pyarena.h header. Rename functions:

* PyArena_New() => _PyArena_New()
* PyArena_Free() => _PyArena_Free()
* PyArena_Malloc() => _PyArena_Malloc()
* PyArena_AddPyObject() => _PyArena_AddPyObject()

Remove parser functions using the "struct _mod" type, because the
AST C API was removed:

* PyParser_ASTFromFile()
* PyParser_ASTFromFileObject()
* PyParser_ASTFromFilename()
* PyParser_ASTFromString()
* PyParser_ASTFromStringObject()

These functions were undocumented and excluded from the limited C
API.

Add pycore_parser.h internal header file. Rename functions:

* PyParser_ASTFromFileObject() => _PyParser_ASTFromFile()
* PyParser_ASTFromStringObject() => _PyParser_ASTFromString()

These functions are no longer exported (replace PyAPI_FUNC() with
extern).

Remove also _PyPegen_run_parser_from_file() function. Update
test_peg_generator to use _PyPegen_run_parser_from_file_pointer()
instead.

Include/{odictobject.h,parser_interface.h,picklebufobject.h,pydebug.h,pyfpe.h}
into Include/cpython/.

Parser: peg_api: include Python.h instead of parser_interface.h.

Move non-limited C API headers pyarena.h and pyctype.h
into Include/cpython/ directory.

This change is backward compatible since C extension modules
must not include "pytime.h" directly, but only include "Python.h".

Rename PyPegen* functions to PyParser*, so that we can remove the
old set of PyParser* functions that were using the old parser.