gh-132042: Prebuild mro_dict for find_name_in_mro to speedup class creation

Objects/typeobject.c

@@ -11460,10 +11460,7 @@ fixup_slot_dispatchers(PyTypeObject *type)
 {
     int res = 0;
 
-    // This lock isn't strictly necessary because the type has not been
-    // exposed to anyone else yet, but update_ont_slot calls find_name_in_mro
-    // where we'd like to assert that the type is locked.
-    BEGIN_TYPE_LOCK();
+    ASSERT_WORLD_STOPPED_OR_NEW_TYPE(type);
 
     PyObject *mro = Py_NewRef(lookup_tp_mro(type));
 
@@ -11506,7 +11503,7 @@ fixup_slot_dispatchers(PyTypeObject *type)
     Py_XDECREF(mro_dict);
     Py_DECREF(mro);
 
-    END_TYPE_LOCK();
+    // END_TYPE_LOCK();
     return res;
 }