call_method() now uses _PyObject_FastCall()

Issue #29233: Replace the inefficient _PyObject_VaCallFunctionObjArgs() with
_PyObject_FastCall() in call_method() and call_maybe().

Only a few functions call call_method() and call it with a fixed number of
arguments. Avoid the complex and expensive _PyObject_VaCallFunctionObjArgs()
function, replace it with an array allocated on the stack with the exact number
of argumlents.

It reduces the stack consumption, bytes per call, before => after:

test_python_call: 1168 => 1152 (-16 B)
test_python_getitem: 1344 => 1008 (-336 B)
test_python_iterator: 1568 => 1232 (-336 B)

Remove the _PyObject_VaCallFunctionObjArgs() function which became useless.
Rename it to object_vacall() and make it private.

Objects/abstract.c

@@ -2700,8 +2700,8 @@ _PyObject_CallMethodId_SizeT(PyObject *obj, _Py_Identifier *name,
     return retval;
 }
 
-PyObject *
-_PyObject_VaCallFunctionObjArgs(PyObject *callable, va_list vargs)
+static PyObject *
+object_vacall(PyObject *callable, va_list vargs)
 {
     PyObject *small_stack[_PY_FASTCALL_SMALL_STACK];
     PyObject **stack;
@@ -2767,7 +2767,7 @@ PyObject_CallMethodObjArgs(PyObject *callable, PyObject *name, ...)
     }
 
     va_start(vargs, name);
-    result = _PyObject_VaCallFunctionObjArgs(callable, vargs);
+    result = object_vacall(callable, vargs);
     va_end(vargs);
 
     Py_DECREF(callable);
@@ -2791,7 +2791,7 @@ _PyObject_CallMethodIdObjArgs(PyObject *obj,
     }
 
     va_start(vargs, name);
-    result = _PyObject_VaCallFunctionObjArgs(callable, vargs);
+    result = object_vacall(callable, vargs);
     va_end(vargs);
 
     Py_DECREF(callable);
@@ -2805,7 +2805,7 @@ PyObject_CallFunctionObjArgs(PyObject *callable, ...)
     PyObject *result;
 
     va_start(vargs, callable);
-    result = _PyObject_VaCallFunctionObjArgs(callable, vargs);
+    result = object_vacall(callable, vargs);
     va_end(vargs);
 
     return result;