Update bubble bar location in shell

Send wmshell updates about bubble bar position when it is dragged
across the center divide.

Bug: 330585397
Flag: ACONFIG com.android.wm.shell.enable_bubble_bar DEVELOPMENT
Test: manual
  - with bubble bar on home screen
      - long press and drag bubble bar around on same side, no drop
        target
      - release the bubble bar, it snaps back to the original position
      - long press and drag bubble bar to other side, see drop target at
        the corner
      - release bubble bar, it snaps to the new side
      - long press and drag bubble bar to other side and back, see the
        drop target visible, release, snaps back to the original
        position
  - repeat above steps from an app, swipe up taskbar for bubble bar
Change-Id: I88faf641b9c07a19cfbb7a1feb8170a64269ac1f