wayland: Scale saved rect changing monitor scale

The saved rect is used to restore a saved window size. We need to
update this when the window is moved to a monitor with different scale,
so that if we unmaximize a window which was moved to a different
monitor while maximized (for example when unplugged) will restore to
the correct size.

https://bugzilla.gnome.org/show_bug.cgi?id=755097