Message 287143 - Python tracker

Proposed patch renames METH_FASTCALL to METH_FASTCALL|METH_KEYWORDS and makes bare METH_FASTCALL be used for functions with positional-only parameters. This eliminates small cost that these functions pay for handling empty keywords: calling _PyStack_UnpackDict() and _PyArg_NoStackKeywords(), passing kwnames. This also can slightly reduce stack consumption.