Additional Tests for DefaultClock

DefaultClock needed additional units as coverage of much of that class
was too low. This additionally adds an animation disable flag into
AnimatableClockView for use by the screenshot test.

Bug: 229771520
Test: atest DefaultClockProviderTest
Change-Id: I7d585cedb9b43ac0fb6405e36bec99ee8a246a61
(cherry picked from commit a823b466)