docs: Warn users of ClutterGeometry
docs: Warn users of ClutterGeometry

The Geometry type is an *awful* representation of a integer rectangle,
as it uses unsigned integers for its size, leading to overflow issues
when unioning and intersecting. We have better rectangle types in
Cairo and Clutter, these days.

djdeath/clutter-android,Distrotech/clutter,ebassi/clutter,heysion/clutter-clone,heysion/clutter-clone,collects/clutter,Distrotech/clutter,ebassi/clutter,GNOME/clutter,collects/clutter,collects/clutter,heysion/clutter-clone,djdeath/clutter-android,jigpu/clutter,jigpu/clutter,djdeath/clutter,jigpu/clutter,Distrotech/clutter,djdeath/clutter-android,djdeath/clutter-android,djdeath/clutter,jigpu/clutter,djdeath/clutter,Distrotech/clutter,jigpu/clutter,Distrotech/clutter,ebassi/clutter,jigpu/clutter,ebassi/clutter,collects/clutter,djdeath/clutter,djdeath/clutter,Distrotech/clutter,GNOME/clutter,heysion/clutter-clone,collects/clutter,GNOME/clutter,djdeath/clutter-android,GNOME/clutter,djdeath/clutter,heysion/clutter-clone,GNOME/clutter,ebassi/clutter