wayland: Scale window geometry rects given the main output

Since we scale surface actors given what main output their toplevel
window is on, also scale the window geometry coordinates and sizes
(window->rect size and window->custom_frame_extents.top/left) in order
to make the window geometry represent what is being rendered on the
stage.

https://bugzilla.gnome.org/show_bug.cgi?id=744934