Fix gesture exclusion for bubbles

This was happening after the stack was dismissed & came
back. I think the onDrawListener should be added / removed
when BSV is attached/detached.

We reuse BubbleStackView in S so this is probably a
regression from those changes.

Fixes: 181083993
Test: 1 - have gesture nav enabled
      2 - add bubbles, dismiss them, add more
      3 - check that bubbles are easily moveable & don't
          trigger back
Change-Id: I1176efd2e41b3c9f1adb0d756e03bcfc5837eab6