x11/stage: fix multi-stage support
x11/stage: fix multi-stage support

When handling Configure events from the X server we update the
internal copy of the window size. Unfortunately we may be updating the
wrong stage implementation because we use the one related to the event
translator (which is the first created stage).

This patch fix flickering/redrawning issues with multi-stage by
looking for the right stage implementation associated with an XEvent.

Signed-off-by: Lionel Landwerlin <9463032a5b99ffad10f36631678a833369a311b5@linux.intel.com>

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