Set bubble bar aligned to QSB

Change logic to updated bubble bar alignment with the QSB vertical
center for 3 buttons navigation mode.

Fixes: 378400160
Flag: com.android.wm.shell.enable_bubble_bar
Test: PersistentBubbleStashControllerTest
Test: TransientBubbleStashControllerTest
Test: Manual. Set the buttons navigation mode and observe that the
bubble bar is centered with the QSB when the QSB is not aligned with the
hotseat. Then, switch to gestures navigation mode and observe that the
bubble bar is centered with the hotseat when the QSB is not aligned with
the hotseat.

Change-Id: I57a32ac5bde7a7055b54a89727429424e5c0ca4f