clutter/actor: Round to 256ths when projecting for picking

Picking is specially sensitive for float precision, and tests can
easily fail when something changes, even if ever so slightly. A
simple way to workaround this is by adjusting the projected points
using the same procedure described at 67cc60cbda.

Round projected points for picking to 256ths.

https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1489

clutter/clutter/clutter-actor.c

@@ -1294,6 +1294,9 @@ _clutter_actor_transform_local_box_to_stage (ClutterActor          *self,
                                           &vertices[v].y,
                                           &z,
                                           &w);
+
+      clutter_round_to_256ths (&vertices[v].x);
+      clutter_round_to_256ths (&vertices[v].y);
     }
 
   return TRUE;