[3.14] gh-134160: Split extension module init from PyModule docs; emphasize multi-phase init (GH-135126)

[miss-islington]

Document behaviour of single-phase init. Call it "legacy".

Reorganize PyModule docs.

Move PyInit_modulename docs from the tutorial to reference documentation.

Move PyMODINIT_FUNC docs from generic macros to the new page.

Add doc stubs for PYTHON_API_VERSION & PYTHON_ABI_VERSION

Remove incorrect refcounts.dat entry for PyModuleDef_Init.
This removes the "Return value: Borrowed reference." note.
Instead, note that the function sometimes returns a borrowed reference,
sometimes as strong one.
(IMO, it's best to not think of PyModuleDef as a PyObject at all,
and act like it can't be reference-counted.)

(cherry picked from commit f4bc3a9)

Co-authored-by: Petr Viktorin [email protected]
Co-authored-by: Adam Turner [email protected]
Co-authored-by: Stan Ulbrych [email protected]
Co-authored-by: Hugo van Kemenade [email protected]

• Issue: Docs Examples Focus on Outdated Single-Phase Init Modules and Static Types #134160

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