gh-102304: Fix Py_INCREF() stable ABI in debug mode (#104763)

When Python is built in debug mode (if the Py_REF_DEBUG macro is
defined), the Py_INCREF() and Py_DECREF() function are now always
implemented as opaque functions to avoid leaking implementation
details like the "_Py_RefTotal" variable or the
_Py_DecRefTotal_DO_NOT_USE_THIS() function.

* Remove _Py_IncRefTotal_DO_NOT_USE_THIS() and
  _Py_DecRefTotal_DO_NOT_USE_THIS() from the stable ABI.
* Remove _Py_NegativeRefcount() from limited C API.