clutter: Move redraw clip management to views

The stage window handled the redraw clip in a global manner; this would
interfere if we want to paint views individually as it'd mean
intersecting views (i.e. mirrored monitors) would loose the redraw clip
once the first view was painted. It also is awkward to have a global
state for something that is built up before redrawing, and only really
valid during paint, due to buffer damage history.

This commits removes all redraw clip management from the stage window,
moving it all into the stage views. When a redraw clip is added to the
stage, every affected view will get the same redraw clip added to it,
and eventually when painted, the stage window (ClutterStageCogl) will
retrieve the redraw clip for each view as it repaints them.

https://gitlab.gnome.org/GNOME/mutter/merge_requests/1042

clutter/clutter/clutter-util.c

@@ -214,6 +214,16 @@ _clutter_util_rectangle_intersection (const cairo_rectangle_int_t *src1,
     }
 }
 
+gboolean
+clutter_util_rectangle_equal (const cairo_rectangle_int_t *src1,
+                              const cairo_rectangle_int_t *src2)
+{
+  return ((src1->x == src2->x) &&
+          (src1->y == src2->y) &&
+          (src1->width == src2->width) &&
+          (src1->height == src2->height));
+}
+
 float
 _clutter_util_matrix_determinant (const ClutterMatrix *matrix)
 {