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

Add new trashcan macros to deal with a double deallocation that could occur when the `tp_dealloc` of a subclass calls the `tp_dealloc` of a base class and that base class uses the trashcan mechanism.

Patch by Jeroen Demeyer.

This speeds up pickling of some iterators.

This fixes also error handling in pickling methods when fail to
look up builtin "getattr".

Fix invalid function cast warnings with gcc 8
for method conventions different from METH_NOARGS, METH_O and
METH_VARARGS excluding Argument Clinic generated code.

Move _PyObject_GC_TRACK() and _PyObject_GC_UNTRACK() from
Include/objimpl.h to Include/internal/pycore_object.h.

Rename Include/internal/ headers:

* pycore_hash.h -> pycore_pyhash.h
* pycore_lifecycle.h -> pycore_pylifecycle.h
* pycore_mem.h -> pycore_pymem.h
* pycore_state.h -> pycore_pystate.h

Add missing headers to Makefile.pre.in and PCbuild:

* pycore_condvar.h.
* pycore_hamt.h
* pycore_pyhash.h

If Py_BUILD_CORE is defined, the PyThreadState_GET() macro access
_PyRuntime which comes from the internal pycore_state.h header.
Public headers must not require internal headers.

Move PyThreadState_GET() and _PyInterpreterState_GET_UNSAFE() from
Include/pystate.h to Include/internal/pycore_state.h, and rename
PyThreadState_GET() to _PyThreadState_GET() there.

The PyThreadState_GET() macro of pystate.h is now redefined when
pycore_state.h is included, to use the fast _PyThreadState_GET().

Changes:

* Add _PyThreadState_GET() macro
* Replace "PyThreadState_GET()->interp" with
  _PyInterpreterState_GET_UNSAFE()
* Replace PyThreadState_GET() with _PyThreadState_GET() in internal C
  files (compiled with Py_BUILD_CORE defined), but keep
  PyThreadState_GET() in the public header files.
* _testcapimodule.c: replace PyThreadState_GET() with
  PyThreadState_Get(); the module is not compiled with Py_BUILD_CORE
  defined.
* pycore_state.h now requires Py_BUILD_CORE to be defined.