util: Add a SCREEN_CAST debug topic

This is going to be useful to log dropped frames and other more common
errors about screencasting.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1709>

src/core/main.c

@@ -121,6 +121,7 @@ static const GDebugKey meta_debug_keys[] = {
   { "input", META_DEBUG_INPUT },
   { "wayland", META_DEBUG_WAYLAND },
   { "kms", META_DEBUG_KMS },
+  { "screen-cast", META_DEBUG_SCREEN_CAST },
 };
 
 /*

src/core/util.c

@@ -278,6 +278,8 @@ topic_name (MetaDebugTopic topic)
       return "INPUT";
     case META_DEBUG_KMS:
       return "KMS";
+    case META_DEBUG_SCREEN_CAST:
+      return "SCREEN_CAST";
     case META_DEBUG_VERBOSE:
       return "VERBOSE";
     case META_DEBUG_WAYLAND: