[notif] fix icon coloring logic

two main fixes here:

1. Fix the `viewBounds` calculation. And unify the logic with our
   existing ViewUtil.kt class

2. Remove the optimization(?) of pre-calculating the dark area in the
   iconColors flow from the notif collection view model. I think that
   it's trying to be fancy and avoid calculating region-based tint if it
   doesn't change in a given area of the screen. The problem is that
   sometimes the icons aren't notified that the color actually changed.

Test: ViewUtilTest NotificationIconContainerStatusBarViewModelTest
Test: manual: split screen with dark app on left and light app on right
Bug: 382543507
Flag: EXEMPT bugfix
Change-Id: Ib463b7687a437bef65365b25eeb9757e75d099fa