Fix the overflow button disappearing suddenly during animations

A couple of things going on with this:

1) The overflow visibility was being updated when the expanded view
   animation was finished NOT when the bubble view animation was
   finished, so it would switch to be invisible before it reached
   its final spot.
2) The overflow was being animated to the resting position of
   normal bubble, when really because it disappears we should
   animate it to a spot that wouldn't be visible -- so remove the
   offset applied to its animation. When this is done, it kinda
   bounces behind the top bubble which looks a bit weird so I also
   reduced the bounciness of it.
3) If the overflow is showing the update dot, this also needs to
   be animated in / out so that it doesn't just show / hide.

Test: manual / visual - expand and collapse bubbles it and observe
                        that the overflow originates / returns to the
                        stack rather than suddenly disappearing
                      - check if you only have 1 bubble that the
                        overflow doesn't bounce past the first bubble
                        when collapsing.
Bug: 301270929

Change-Id: I175482388edbb43d0903d0dd420d24ec0e4cb7ea