Switch Bubble Bar side on navigation mode change to 3 buttons.

When user updates to the 3 buttons navigation mode, launcher should
switch the bubble ber to the left side (or to the right if RTL).

Fixes: 346381754
Test: WMShellRobolectricTests
Test: Manual. Have bubble bar on the default side with some bubbles in
gesture mode. Switch to 3 buttons navigation mode. Bubble bar is
moved to the opposite side.
Video: http://recall/-/gx8ASgewUeUS3QYohfrd1J/hH2pQqDOTzQuci4k1N3q99
Flag: com.android.wm.shell.enable_bubble_bar

Change-Id: I6b8dd9fbcf872958a2a305c21241b0c865bbef04