[3.12] gh-107915: Handle errors in C API functions PyErr_Set*() and PyErr_Format() (GH-107918) (#108134)

* gh-107915: Handle errors in C API functions PyErr_Set*() and PyErr_Format() (GH-107918)

Such C API functions as PyErr_SetString(), PyErr_Format(),
PyErr_SetFromErrnoWithFilename() and many others no longer crash or
ignore errors if it failed to format the error message or decode the
filename. Instead, they keep a corresponding error.
(cherry picked from commit 633ea217a85f6b6ba5bdbc73094254d5811b3485)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>

* Define PY_SSIZE_T_CLEAN.

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Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>