gh-135755: Docs: C API: Document missing PyFunction_GET* macros

[ZeroIntensity]

I'm documenting all of these before getting to PyFunction_GET_BUILTINS, because this needs to be backported to 3.13. I'll document PyFunction_GET_BUILTINS in a follow-up that goes only to 3.14.

I've included versionadded directives for a few APIs that were added in 3.0 (PEP-3102 and PEP-3107), but I don't know if those are particularly useful these days. AFAIK, it's a controversial topic.

• Issue: Undocumented 3.14 C API #135755

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📚 Documentation preview 📚: https://cpython-previews--135762.org.readthedocs.build/en/135762/c-api/function.html#function-objects

[picnixz]

I'd appreciate if we have the "Return value: borrowed reference" for those functions (i.e., update refcounts.dat to add those entries).

[picnixz]

Looks good now: