Set bubble bar alpha to 0 and collapse if it bubbles are hidden

Only set bubble bar alpha to 0 and mark it collapsed when bubbles are
hidden.
When bubble bar should be hidden due to system ui state, only update
visibility.

Bug: 324068295
Flag: ACONFIG com.android.wm.shell.enable_bubble_bar DEVELOPMENT
Test: trigger a buble from bubbles test app
  - swipe to home screen
  - observe bubble bar is shown
  - swipe notification shade down and away again
  - observe bubble bar is hidden when shade is open, and shown when
    closed
  - expand bubble bar
  - repeat swipe shade down and away, observe expanded bubble is hidden
    while shade is open and bubble is expanded when shade is swiped away
Change-Id: Icc717ab250061f14f02a558eb9f7301fdc08c5c7