Color Change Animation for AnimatableClockView

Creating a simple color fade animation for when theme or region
sampling changes the color of the clock. This replaces the use of
animateAppearOnLockscreen() for those cases by creating a specific animation that only deals with color.

Fixes: 259282866
Test: manual
Change-Id: I279b5e01025a0f7bf5815599ea786a1ab68c06ef