trap shaped x11 clients and prevent compositor blocking with high rect count

trap shaped x11 clients and prevent compositor blocking with high rect count

in the case where a shaped window with many rects exists, there is a high
probability of the damage rect count being huge, leading to massive blocking for
each frame as the compositor attempts to fetch all of these rects from the xserver.

instead, the compositor can shortcut this by forcing a full-window damage any time
the rect count is sufficiently high, trading a blocking socket operation for some
amount of (potential) overdraw.

testing in affected scenarios has shown huge improvements: where previously the entire
compositor would lock up, things work as expected now

see https://bugzilla.mozilla.org/show_bug.cgi?id=1214746 for a sample case