Remove private _PyThreadState and _PyInterpreterState C API functions: move them to the internal C API (pycore_pystate.h and pycore_interp.h). Don't export most of these functions anymore, but still export functions used by tests. Remove _PyThreadState_Prealloc() and _PyThreadState_Init() from the C API, but keep it in the stable API.
Miscellaneous source files for the main Python shared library