PyAPI: add load_factory_startup_post handler

Needed so we can apply changes to the startup file,
only in the case when it's load loaded from a user-saved startup.

source/blender/python/intern/bpy_app_handlers.c

@@ -66,6 +66,7 @@ static PyStructSequence_Field app_cb_info_fields[] = {
 	{(char *)"depsgraph_update_pre",  (char *)"on depsgraph update (pre)"},
 	{(char *)"depsgraph_update_post", (char *)"on depsgraph update (post)"},
 	{(char *)"version_update",        (char *)"on ending the versioning code"},
+	{(char *)"load_factory_startup_post", (char *)"on loading factory startup (after)"},
 
 	/* sets the permanent tag */
 #   define APP_CB_OTHER_FIELDS 1