Fixing some minor issues in accessibility focus.

1. Now accessibility focus does not drag input focus and
   vice versa. Having the two focuses chase each other
   can lead to some pathological cases. For example, a
   container is input focusable and manages input focus
   for its children i.e. as soon as it gets input focus
   it sets input focus to a child. Now assume input and
   accessibility focus are on a child and focus search
   finds the parent to take accessibility focus, now
   putting accessibility focus to the parent will put
   input focus there and the parent will put input focus
   to the child which as a result will put accessibility
   focus there, thus resulting in traversal loop.

bug:6522900

2. Fixed asymmetrical behavior of accessibility focus search
   for AbsListView.

bug:6520016e

3. Fixed accessibility focus search getting stuck in an
   empty AbsListView.

bug:6520049

Change-Id: Ia26e5be7b5a9f340f873861ff466c787467b98dc