actor: add oob-transform opt to catch out-of-band transforms

Out-of-band transforms are considered to be all actor transforms done
directly with the Cogl API instead of via ClutterActor::apply_transform.

By running with CLUTTER_DEBUG=oob-transform then Clutter will explicitly
try to detect when un-expected transforms have been applied to the
modelview matrix stack.

Out-of-band transforms can lead to awkward bugs in Clutter applications
because Clutter itself doesn't know about them and this can disrupt
Clutter's input handling and calculations of actor paint-volumes
which can lead to visual artifacts.

Reviewed-by: Emmanuele Bassi <ebassi@linux.intel.com>

clutter/clutter-debug.h

@@ -26,7 +26,8 @@ typedef enum {
   CLUTTER_DEBUG_LAYOUT              = 1 << 15,
   CLUTTER_DEBUG_PICK                = 1 << 16,
   CLUTTER_DEBUG_EVENTLOOP           = 1 << 17,
-  CLUTTER_DEBUG_CLIPPING            = 1 << 18
+  CLUTTER_DEBUG_CLIPPING            = 1 << 18,
+  CLUTTER_DEBUG_OOB_TRANSFORMS      = 1 << 19
 } ClutterDebugFlag;
 
 typedef enum {