This adds feature flags if a backend supports auto rotations. While this is not
directly a function of a backend on X11 auto rotation is not tested fully yet
and there are problems with touch input. This way a client can query if auto
rotation is fully functional on a backend.

For the KWayland backend auto rotation and tablet mode information querying is
already wired up but for now deactivated until all KWin patches have been
landed.

Compiles and tests with an XPS 2-in-1, which sadly does not send events about
the tablet state.