Add _PyObject_VaCallFunctionObjArgs() private function

Issue #28915: Similar to _PyObject_CallFunctionObjArgs() but use va_list to
pass arguments.

Include/abstract.h

@@ -437,6 +437,12 @@ PyAPI_FUNC(PyObject *) _PyObject_CallMethodId_SizeT(PyObject *obj,
 PyAPI_FUNC(PyObject *) PyObject_CallFunctionObjArgs(PyObject *callable,
                                                     ...);
 
+#ifndef Py_LIMITED_API
+PyAPI_FUNC(PyObject *) _PyObject_VaCallFunctionObjArgs(
+    PyObject *callable,
+    va_list vargs);
+#endif
+
   /*
 Call the method named 'name' of object 'obj' with a variable number of
 C arguments.  The C arguments are provided as PyObject *