Lock/disable panel autorotation with touch-mode disabled

Expose panel auto orientation handling in a PanelOrientationManaged readonly property in org.gnome.Mutter.DisplayConfig, so that we can apply a centralized policy for the whole mutter/gnome-shell/gnome-control-center trio.

With this in place, we can involve the ClutterSeat::touch-mode property, so we only autorotate if touch-mode is enabled (eg. 2-in-1s with a detached keyboard). In laptop mode, the automatic rotation would be disabled, and presumably should be allowed to do manually like in regular laptops.