docs: Improve deprecation notices for ClutterRectangle
docs: Improve deprecation notices for ClutterRectangle

Distrotech/clutter,jigpu/clutter,GNOME/clutter,Distrotech/clutter,Distrotech/clutter,GNOME/clutter,Distrotech/clutter,jigpu/clutter,Distrotech/clutter,GNOME/clutter,GNOME/clutter,jigpu/clutter,jigpu/clutter,jigpu/clutter,Distrotech/clutter,GNOME/clutter,jigpu/clutter