bpo-39573: Py_TYPE becomes a static inline function

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Convert the Py_TYPE() and Py_SIZE() macros to static inline
functions. The Py_SET_TYPE() and Py_SET_SIZE() functions must now be
used to set an object type and size.

https://bugs.python.org/issue39573

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One year ago, I already pushed the same change to Python 3.10, but it broke many projects and so had to be reverted, see: https://bugs.python.org/issue39573#msg370074

Multiple things changed since my latest attempt:

• Major projects like Cython and numpy have been prepared for this incompatible change

• I created the https://github.com/pythoncapi/pythoncapi_compat project which is made of two parts:

  • pythoncapi_compat.h header file provides Py_SET_TYPE() and Py_SET_TYPE() to old Python versions: it supports Python 2.7-3.11.
  • upgrade_pythoncapi.py script automates the migration of existing C extensions to the new API (Py_SET_TYPE, Py_SET_TYPE) without losing support with Python 2.7-3.8.

• pythoncapi_compat.h header and upgrade_pythoncapi.py script have been used successfully on multiple projects (bitarray, immutables, Mercurial, python-zstandard). These projects now include a copy of pythoncapi_compat.h to support old Python versions.

Note: C extensions implemented with Cython only have to regenerate the C files using Cython, if it's not already done (Cython was fixed one year ago).

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More info about the pythoncapi_compat project: https://vstinner.github.io/pythoncapi_compat.html

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The previous attempt (reverted change) was: #20290

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I prefer to merge such incompatible change early in 3.11 dev cycle to give more test to users to test it. If things go wild again, we can consider to revert it a second time.