Fix bubble bar location on device boot.

Updated logic to set bubble bar location opposite to navigation bar.

Test: BubblesTest
Test: Manual. Restart the device, observe the navigation bar appears at
default location.
Flag: com.android.wm.shell.enable_bubble_bar
Fixes: 380309079

Change-Id: I6644aebb5a4df77efc897bf22da1e56be5354e73