wayland/lockscreen_overlay: Fix state not being persisted across windows for a single surface

For plasma-mobile!270 (merged)

Currently, when a surface is allowed to be a lockscreen overlay, the property is set on the window. However, when the window is recreated (ex. QML window.visible = false, window.visible = true) and the surface remains the same, this state is lost. See plasma-mobile!270 (comment 1248764)

This MR architecturally is probably not the way to go but I just wanted to get something to work off of for discussion. It adds the lockscreen overlay property on SurfaceInterface, and ensures that Window's property is up to date with the surface.