Transitions - Listen for bouncer show & hide

Was only listening for hide() previously. Add support for show().

Also make sure bouncer is not reported while occluded.

Also, use ::Pair, ::toTriple to reduce code clutter for common
operations

Test: atest KeyguardRepositoryImplTest
KeyguardTransitionRepositoryTest
Test: manual, better integration tests pending for transitions
Bug: 195430376

Change-Id: Ic9cd5a7309bdc26c016e33c4221eb8b7c442c2fa