gh-130396: Move PYOS_LOG2_STACK_MARGIN to internal headers (GH-135928)

Move PYOS_LOG2_STACK_MARGIN, PYOS_STACK_MARGIN,
PYOS_STACK_MARGIN_BYTES and PYOS_STACK_MARGIN_SHIFT macros to
pycore_pythonrun.h internal header. Add underscore (_) prefix to the
names to make them private. Rename _PYOS to _PyOS.
(cherry picked from commit 28940e8e4884eb3444a8ea15a5634f76b154d7ed)

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

This converts functions, code, str, bytes, bytearray, and memoryview objects to PyCodeObject,
and ensure that the object looks like a script.  That means no args, no return, and no closure.
_PyCode_GetPureScriptXIData() takes it a step further and ensures there are no globals.

We also add _PyObject_SupportedAsScript() to the internal C-API.

(cherry picked from commit c81fa2b9cd1ed4d4ff5c13984d6582c27e5f2633, AKA gh-133480)

Co-authored-by: Eric Snow <ericsnowcurrently@gmail.com>

Remove these private functions from the public C API:

* _PyRun_AnyFileObject()
* _PyRun_InteractiveLoopObject()
* _PyRun_SimpleFileObject()
* _Py_SourceAsString()

Move them to the internal C API: add a new pycore_pythonrun.h header
file. No longer export these functions.