util: Add back topic prefix to meta_topic() messages

Was lost when changing to use g_message(); lets add it back.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2125>

src/meta/util.h

@@ -175,7 +175,10 @@ const char * meta_topic_to_string (MetaDebugTopic topic);
     { \
       if (meta_is_topic_enabled (debug_topic)) \
         { \
-          g_message (__VA_ARGS__); \
+          g_autofree char *message = NULL; \
+\
+          message = g_strdup_printf (__VA_ARGS__); \
+          g_message ("%s: %s", meta_topic_to_string (debug_topic), message); \
         } \
     } \
   G_STMT_END