Accessibility focus search and setting it from hover are performed by the client.

1. Currently we are providing accessibility focus search algorithm in the
   framework and we are also setting accessibility focus from hover. It
   appears that implementing a focus search strategy that works for all
   accessibility services is non trivial task if feasible. Based on
   feedback from the developers of two such services at Google - TalkBack
   and BarilleBack - the built in focus search does not quite match what
   they need and they would like to implement a custom strategy.

   Hence, having APIs for accessibility focus search in the framework does
   not make. Therefore, we are hiding this APIs and later will take out the focus
   search logic and allow the accessibility service to implement search.

   Also putting accessibility focus from hover is tightly integrated with
   the focus search since the set of views that get accessibility focus
   from hover should be the same as the set of views returned by the
   focus search routine. Therefore, we are letting the accessibility service
   decide where to put accessibility focus when it gets an accessibility
   hover event.

bug:6675330

Change-Id: Ie152230990a6602f3fd1d82de2177d0b1444d654