Co-authored-by: Jeroen Demeyer <J.Demeyer@UGent.be>
Co-authored-by: Mark Shannon <mark@hotpy.org>

Add METH_STACKLESS to prevent future collisions.

the bare METH_FASTCALL be used for functions with positional-only
parameters.

Calling builtin method is at most 10% faster.

Issue #29259, #29263. methoddescr_call() creates a PyCFunction object, call it
and the destroy it. Add a new _PyMethodDef_RawFastCallDict() method to avoid
the temporary PyCFunction object.

Issue #27810: Add a new calling convention for C functions:

    PyObject* func(PyObject *self, PyObject **args,
                   Py_ssize_t nargs, PyObject *kwnames);

Where args is a C array of positional arguments followed by values of keyword
arguments. nargs is the number of positional arguments, kwnames are keys of
keyword arguments. kwnames can be NULL.