Updated how taskbar touch area is being set.

Included bubble bar bounds to the taskbar touch area instead of
replacing taskbar touch area.

Fixes: 356903636
Flag: com.android.wm.shell.enable_bubble_bar
Test: Manual. Switch to the persistent task bar mode, have bubble. Go to
any application or overview. Task bar icons are touchable.

Change-Id: I3775c2e69a7bf89f1d5223707d7c4c94175fcfa8