Wayland: Provide control over when configuration event ACKs are sent
Given that mutter#1143 (closed) was closed as WONTFIX, games and other low-level programs need a way to draw title bars that integrates well with the rest of the desktop. As per mutter#1143 (comment 750403), this requires GDK to allow applications to control when window manager configuration requests are ACKd, to avoid flickering.