The Vectorcall API (PEP 590) was made public, adding the functions
``PyObject_Vectorcall``, ``PyObject_VectorcallMethod``,
``PyVectorcall_Function``, ``PyObject_CallOneArg``,
``PyObject_CallMethodNoArgs``, ``PyObject_CallMethodOneArg``,
``PyObject_FastCallDict``, and the flag ``Py_TPFLAGS_HAVE_VECTORCALL``.
