bpo-40521: Make list free list per-interpreter (GH-20642)

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.