Hit back button in overflow to collapse stack

getExpandedDisplayId(mContext) was returning -1 (INVALID_DISPLAY) for overflow

Add getDisplayId to BubbleViewProvider, override that in overflow and
return actual display id for overflow's expanded view.

Fixes: 150398525
Fixes: 149882551
Test: manual -> press back button in overflow -> stack collapses
Test: manual -> swipe right from left edge in gesture nav -> stack collapses
Test: adb shell am instrument -w com.android.systemui.tests
Change-Id: I9d43de3803a7c771eaabe38b8e8dc9aacd8bad94