wayland/layershell: add ability to set empty input region

[bbedward]

Adds the ability to set an empty input region on wayland surfaces, which is useful for things like Wallpaper backgrounds.

PanelWindow {
  WlrLayershell.inputMode = WlrInputMode.None
}

Without this, labwc's own input region is unable to receive events, which prevents its integrated desktop/context menus from working as expected. There are probably other use cases for this as well.

I just made it an enum with None and Full (current and default behavior) since I think that's the mai use case, don't see much use case for quickshell being able to support anything beyond that in terms of input regions.

[outfoxxed]

This is already exposed as mask which can be set to an empty region.