Make interface types a string

This is more in line with wayland and it allows us to create new
interfaces in modules without having to add anything to the type
enum. It also removes some lookups to map type_id to readable
name in debug.

src/modules/spa/module-device-factory.c

@@ -77,7 +77,7 @@ static const struct pw_impl_device_events device_events = {
 
 static void *create_object(void *_data,
 			   struct pw_resource *resource,
-			   uint32_t type,
+			   const char *type,
 			   uint32_t version,
 			   struct pw_properties *properties,
 			   uint32_t new_id)