Don't factor animating-to-sleep for nav bar visibility

- Instead, just animate the current nav bar view (which doesn't cause
  insets changes).  This should be safe to do because:
  1) Nothing else animates the alpha of this particular part of the
     view hierarchy
  2) Confirmed with SysUI folks that we always get onStartedWakingUp
     after onStartedGoingToSleep
  3) This otherwise reverts to the same nav bar visibility logic in R

Bug: 196789451
Bug: 190368572
Test: atest StatusBarKeyguardViewManagerTest
Test: In three button nav w/ AOD, turn off the screen
      - also try above with interrupting the screen off animation
      - also try above with power button instantly locks disabled
Change-Id: I1be44a9a8dbb8cea17bbf354a2e03dd4bad5a4a2