C API: Cleanup header files

[vstinner]

Feature or enhancement

Has this already been discussed elsewhere?

No response given

Links to previous discussion of this feature:

No response

Proposal:

Meta issue for a few changes related to C API header files.

Linked PRs

• gh-108765: Reformat Include/pymacconfig.h #108764
• gh-108765: Reformat Include/osdefs.h #108766
• gh-108765: Move standard includes to Python.h #108769
• gh-108765: Python.h no longer includes <sys/time.h> #108775
• gh-108765: Remove legacy prototypes from pyport.h #108776
• gh-108765: Python.h no longer includes <ieeefp.h> #108781
• gh-108765: Remove old prototypes from pyport.h #108782
• gh-108765: Python.h no longer includes <unistd.h> #108783
• gh-108765: [TEST] Test combined Python.h changes #108784
• gh-108765: multiprocessing.h includes <unistd.h> #108823
• gh-108765: include <unistd.h> in termios.c on Solaris #108825
• gh-108765: pystrhex: Replace stdlib.h abs() with Py_ABS() #108830
• gh-108765: Python.h no longer includes <ctype.h> #108831
• gh-108765: Move stat() fiddling from pyport.h to fileutils.h #108854
• gh-108765: Move export code from pyport.h to exports.h #108855
• gh-108765: Cleanup #include in Python/*.c files #108977
• gh-108765: Include explicitly <unistd.h> in signalmodule.c #111402
• gh-108765: Python.h no longer includes <stddef.h> on Windows #111563
• gh-108765: fix comment about macro definitions in _stat.c post GH-108854 #136027
• [3.14] gh-108765: fix comment about macro definitions in _stat.c post GH-108854 (GH-136027) #136043
• [3.13] gh-108765: fix comment about macro definitions in _stat.c post GH-108854 (GH-136027) #136044