Selectively share KeyguardQuickAffordancesCombinedViewModel

Since the indication area and shortcuts section refer to the
same quick affordances, they should share the same model, which
will greatly reduce the number of continuations running.

Also add a bit more logging for when quick affordances update.

Fixes: 360066410
Test: atest PlatformScenarioTests:LockscreenShortcutTest
Flag: EXEMPT bugfix

Change-Id: I6fb579e37f79d8210e86996dda8623654078e645