Update DefaultClockProvider colors

This is largely a cherry-pick of change
I6b32776dac1853eeab87c2a65da69478e4da5b75 but with
some notable changes to accomadate existing code
differences in tm-qpr-dev.

 - We use a boolean instead of an enum for clock region
   darkness as the enum is in a different place in tm-qpr-dev.
 - We clean up some of the initialization code in
   ClockEventController to prevent testing issues and provide
   a dependency injection point to the screenshot test.
 - Pull the clock color setting from the theme when region
   sampling is disabled instead of defaulting to always dark.

Test: Manually validated colors matched reference images on
light and dark backgrounds with the region sampling feature
both enabled and disabled.

Bug: 229771520
Change-Id: I7906850b5de7f512f55e47e1122dfaacbc9c9406
(cherry picked from commit a724e0b7)