Remove the following function from the C API:

* PyAsyncGen_ClearFreeLists()
* PyContext_ClearFreeList()
* PyDict_ClearFreeList()
* PyFloat_ClearFreeList()
* PyFrame_ClearFreeList()
* PyList_ClearFreeList()
* PySet_ClearFreeList()
* PyTuple_ClearFreeList()

Make these functions private, move them to the internal C API and
change their return type to void.

Call explicitly PyGC_Collect() to free all free lists.

Note: PySet_ClearFreeList() did nothing.

Co-Author: Neil Schemenauer <nas-github@arctrix.com>

Move tupleobject.h code surrounded by "#ifndef Py_LIMITED_API"
to a new Include/cpython/tupleobject.h header file.

Add cpython/ header files to Makefile.pre.in and pythoncore project
of PCbuild.

Add "assert(PyTuple_Check(op));" to _PyTuple_CAST() to check that the
argument is a tuple object in debug mode.

PyTuple_GET_SIZE() now uses _PyTuple_CAST() to get its assertion.

Move _PyTuple_ITEMS() to a new header file:
Include/internal/pycore_tupleobject.h

* _PyTuple_ITEMS() gives access to the tuple->ob_item field and cast the
  first argument to PyTupleObject*. This internal macro is only usable if
  Py_BUILD_CORE is defined.
* Replace &PyTuple_GET_ITEM(ob, 0) with _PyTuple_ITEMS(ob).
* Replace PyTuple_GET_ITEM(op, 1) with &_PyTuple_ITEMS(ob)[1].