Each interpreter now has its own asynchronous generator free lists:

* Move async gen free lists into PyInterpreterState.
* Move _PyAsyncGen_MAXFREELIST define to pycore_interp.h
* Add _Py_async_gen_state structure.
* Add tstate parameter to _PyAsyncGen_ClearFreeLists
  and _PyAsyncGen_Fini().

Each interpreter now has its own list free list:

* Move list numfree and free_list into PyInterpreterState.
* Add _Py_list_state structure.
* Add tstate parameter to _PyList_ClearFreeList()
  and _PyList_Fini().
* Remove "#ifdef EXPERIMENTAL_ISOLATED_SUBINTERPRETERS".
* _PyGC_Fini() clears gcstate->garbage list which can be stored in
  the list free list. Call _PyGC_Fini() before _PyList_Fini() to
  prevent leaking this list.

Each interpreter now has its own frame free list:

* Move frame free list into PyInterpreterState.
* Add _Py_frame_state structure.
* Add tstate parameter to _PyFrame_ClearFreeList()
  and _PyFrame_Fini().
* Remove "#if PyFrame_MAXFREELIST > 0".
* Remove "#ifdef EXPERIMENTAL_ISOLATED_SUBINTERPRETERS".

Each interpreter now has its own slice cache:

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

Each interpreter now has its own float free list:

* Move tuple numfree and free_list into PyInterpreterState.
* Add _Py_float_state structure.
* Add tstate parameter to _PyFloat_ClearFreeList()
  and _PyFloat_Fini().

Each interpreter now has its own tuple free lists:

* Move tuple numfree and free_list arrays into PyInterpreterState.
* Define PyTuple_MAXSAVESIZE and PyTuple_MAXFREELIST macros in
  pycore_interp.h.
* Add _Py_tuple_state structure. Pass it explicitly to tuple_alloc().
* Add tstate parameter to _PyTuple_ClearFreeList()
* Each interpreter now has its own empty tuple singleton.

Work on a local variable before filling _Py_Identifier members.

Calling PyDict_GetItem() without GIL held had been allowed for
historical reason. It is no longer allowed.