gh-106320: Re-add some PyLong/PyDict C-API functions (GH-#111162)

* gh-106320: Re-add _PyLong_FromByteArray(), _PyLong_AsByteArray() and _PyLong_GCD() to the public header files since they are used by third-party packages and there is no efficient replacement.

See https://github.com/python/cpython/issues/111140
See https://github.com/python/cpython/issues/111139

* gh-111262: Re-add _PyDict_Pop() to have a C-API until a new public one is designed.