Instead of having everyone check net.hadess.SensorProxy themselves, have
this all controlled by the MetaOrientationManager, and proxied everywhere
else via a readonly property in org.gnome.Mutter.DisplayConfig.

We want to attach more complex policies here, and it seems better to
centralize the handling of the autorotation feature rather than
implementing policy changes all over the place.

Based on mutter commit:
GNOME/mutter@1acf7444