Improve enum_param

Add an argument to pass the result param to the caller instead of
having the caller have to pick it up from the builder.
Improve docs for node, clock and monitor
Pass spa_pod everywhere instead of spa_pod_object.
Pass result argument to spa_pod_filter to make things a little
nicer.

src/modules/module-flatpak.c

@@ -434,7 +434,7 @@ do_create_link(void *data,
 	       uint32_t output_port_id,
 	       uint32_t input_node_id,
 	       uint32_t input_port_id,
-	       const struct spa_pod_object *filter,
+	       const struct spa_pod *filter,
 	       const struct spa_dict *props,
 	       uint32_t new_id)
 {