xembedsniproxy: Set input region when hidden to avoid grabbing clicks
xembedsniproxy is a hidden window. It is used for grabbing content and replaying events. It tried to hide itself by adjusting the stacking order.
This is insufficient on wayland where we might be the lowest X window, but that can still be above the desktop. Instead set an empty shape when we should be hidden.
Test plan
Had a floating compact panel (this is important as it means the system tray icon moves about when I open new windows)
Ran hexchat and clicked on the icon and and other icons.
xembedsniproxy was compiled with "VISUAL_DEBUG" flag enabled so I could see where to click, and now (with XWayland >= 2.41) events are never intercepted from the panel.
Bugs fixed
Edited by David Edmundson