Transitions - Refactor view model

All view models were following the same pattern, so consolidate into
KeyguardTransitionAnimationFlow. This also adds support for
cancel/finish events.

Rework how tests run for this. Explicity test logic for how animation
turn into flows with KeyguardTransitionAnimationFlowTest. For the
ViewModels, don't retest this logic, simply verify that the output
stays in the expected range.

Fixes: 266680387
Test: atest
frameworks/base/packages/SystemUI/tests/src/com/android/systemui/keyguard/

Change-Id: I254d213026775e34c0852675ea14efb167271915