Use androidx LifecycleObserver for wiring up controller lifecycles.

DashboardFragment automatically wires up Controllers that implement the
deprecated settingslib LifecycleObserver. Now it can also work for those
that implement the androidx version. The settingslib LifecycleObserver
extends the androidx one, so existing behaviour is preserved.

Bug: 169455298
Test: manual - lifecycles work automatically for such Controllers
Test: manual - no duplicate lifecycle events for existing Controllers
Change-Id: I39ac69f24bf8577867ba3b7e56f96c5f38722a2f