pulse-server: make separate index

Separate the id (the pipewire object id) from the index (what we send to
the client to identify the objects).

src/modules/module-protocol-pulse/manager.h

@@ -79,6 +79,7 @@ struct pw_manager_object {
 	uint32_t permissions;
 	const char *type;
 	uint32_t version;
+	uint32_t index;
 	struct pw_properties *props;
 	struct pw_proxy *proxy;
 	char *message_object_path;