Center bubbles in landscape

BubbleController - listen for orientation change
BubbleStackView, on change - update effective row width; if expanded,
redraw bubble row and pointer

Fixes: 135472021
Bug: 135487618
Test: manual (bubbles remain centered going between portrait and landscape)
Test: manual (bubbles expand to correct positions in portrait and landscape)
Test: atest SystemUITests
Change-Id: I815cd426e26b84b8bd8736dcf16f2119584ecf30