gh-107603: Argument Clinic: Only include pycore_gc.h if needed

[vstinner]

Argument Clinic now only includes pycore_gc.h if PyGC_Head is needed, and only includes pycore_runtime.h if _Py_ID() is needed.

• Add 'condition' optional argument to Clinic.add_include().
• deprecate_keyword_use() includes pycore_runtime.h when using the _PyID() function.
• Fix rendering of includes: comments start at the column 35.
• Mark PC/clinic/_wmimodule.cpp.h and "Objects/stringlib/clinic/*.h.h" header files as generated in .gitattributes.

Effects:

• 42 header files generated by AC no longer include the internal C API, instead of 4 header files before. For example, Modules/clinic/_abc.c.h no longer includes the internal C API.
• Fix _testclinic_depr.c.h: it now always includes pycore_runtime.h to get _Py_ID().

• Issue: Argument Clinic includes internal headers in generated output unconditionally #107603

[vstinner]

@AlexWaygood: Please review my updated PR. I addressed your latest review.

[erlend-aasland]

I also don't like to pass around clinic like that, but if Alex is fine with it, it's ok.

It is nice to avoid unneeded includes, so thanks for that clean-up.

[vstinner]

I also don't like to pass around clinic like that, but if Alex is fine with it, it's ok.

In general, limited_capi bool is now passed as an argument. clinic is only passed as an argument when clinic.add_include() should be called.

[AlexWaygood]

LGTM

I also don't like to pass around clinic like that

Yeah, agreed that this maybe isn't the best pattern, but we can always refactor at a later date — I think this is fine for now.

Thanks for the updates @vstinner!

[vstinner]

Merged, thanks for reviews @AlexWaygood and @erlend-aasland!