Move overflow bubble to stack on update

BubbleData#getOrCreateBubble is called per update, pre-inflation
- If bubble overflowed, remove it from overflow list,
- add it to pending bubbles, where it will be removed on
notificationEntryUpdated, post inflation
- return this bubble instead of creating a new one

Fixes: 150396294
Test: atest SystemUITests
Test: manual
1. Add people bubbles
2. Add more bubbles to get people in overflow
3. Add bubbles for same people, so that they are "active" in stack
4. Go to overflow => overflow no longer shows people "active" in stack

Change-Id: I79c1ba92533169da0e82414f2ad507cbf20d8561