fix new shadow update repaints

resetting is no longer needed with philip layer changes and actually
breaks damages on simultaneous resizes
also use addLayerRepaint for the shadow update

REVIEW: 104306

toplevel.cpp

@@ -381,9 +381,8 @@ void Toplevel::getShadow()
     if (hasShadow())
         dirtyRect |= shadow()->shadowRegion().boundingRect();
     if (dirtyRect.isValid()) {
-        resetRepaints();
         dirtyRect.translate(pos());
-        workspace()->addRepaint(dirtyRect);
+        addLayerRepaint(dirtyRect);
     }
 }