Fix crash when opening bubble overflow

BubbleExpandedView needs a BubbleStackView reference, without that
there could be an NPE in various locations.

Also uses the correct parent view to setup the overflow.

Test: manual - tap on the overflow, observe no crash
Fixes: 150394526
Change-Id: Ib1ae9353a0dfd60ac8b6eb4f94b5b0cc5bc47811