New pipeline: Separate stability rules for group pruning from group changing

Group changes for alerting children are allowed under the stability manager rules, but we were using the same method to determine if the group as a whole could be pruned, but that shouldn't actually be allowed for alerting summaries - it results in the weird unstable animation (and is a regression from S).

Though I made this change more cleanly, the effective delta of this change is just a boolean logic change from:
  isGroupChangeAllowed = isReorderingAllowed || isEntryAlerting
to:
  isGroupChangeAllowed = isReorderingAllowed || (isEntryAlerting && !isPruning)

Fixes: 230734197
Test: atest VisualStabilityCoordinatorTest ShadeListBuilderTest
Change-Id: Ib1a927de2b4cc9b614be29deaf9754c2dc79390f