BubbleData [5/n]: Split up StackView.setExpandedBubble

This splits setSelectedBubble into two discrete steps,
setSelectedBubble, and setExpanded. These will allow
BubbleData to dispatch these actions independently.

Bug: 123542488
Test: atest BubbleControllerTest
Change-Id: I7393d06b08713dc966acd96e165d32ff1e8110f3