Consider the clock detached if the keyguard isn't visible

Update AnimatableClockController's definition of attached to include
whether the keyguard is visible or not. This way, we won't animate
if the view isn't actually visible & we'll reset the clock state when
the keyguard is newly visible.

Only create a new AnimatableClockController onInit instead of
in the onAttach method for KeyguardClockSwitchController.

Fixes: 188203771
Test: manual
Change-Id: Id02132dba8b5392046cb46766aa64fd58e04a4ad