Pass the current interpreter (interp) rather than the current Python
thread state (tstate) to internal functions which only use the
interpreter.

Modified functions:

* _PyXXX_Fini() and _PyXXX_ClearFreeList() functions
* _PyEval_SignalAsyncExc(), make_pending_calls()
* _PySys_GetObject(), sys_set_object(), sys_set_object_id(), sys_set_object_str()
* should_audit(), set_flags_from_config(), make_flags()
* _PyAtExit_Call()
* init_stdio_encoding()
* etc.

Use _PyLong_GetZero() and _PyLong_GetOne()
in Objects/ and Python/ directories.

Add get_xxx_state() function to factorize duplicated code.

Each interpreter now has its own slice cache:

* Move slice cache into PyInterpreterState.
* Add tstate parameter to _PySlice_Fini().

If only offsetof() is needed: include stddef.h instead.

When structmember.h is used, add a comment explaining that
PyMemberDef is used.

Add _PyIndex_Check() function to the internal C API: fast inlined
verson of PyIndex_Check().

Add Include/internal/pycore_abstract.h header file.

Replace PyIndex_Check() with _PyIndex_Check() in C files of Objects
and Python subdirectories.

For example, rename PyTuple_Fini() to _PyTuple_Fini().

These functions are only declared in the internal C API.

Automatically replace
tp_print -> tp_vectorcall_offset
tp_compare -> tp_as_async
tp_reserved -> tp_as_async