Sysui bubbles multiuser fixes: persistence / overflow

* Persist bubbles per-user - rather than one list the
  XML now has a list per-user. The entries in these lists
  still include userId for workprofile since bubbles are
  mixed in the stack / overflow for workprofile.
* When loading bubbles, only the ones for the current user
  are loaded / hit bubbleController code
* When user changes, overflow data should be re-loaded
* Allow the bubble window to be visible for all users

Test: atest BubbleXmlHelperTest BubbleVolatileRepositoryTest
BubblePersistentRepositoryTest BubblesTest
Bug: 173408780

Change-Id: I88cb7cc7ee676d8e0756328a95a54fdaf018a013