Fix backwards compatibility for introspected windows.

1. The APIs for introspecting interactive windows were reporting only
   the touchable windows but were missing the focused window. The user
   can interact with the latter by typing, hence it should always be
   reported. Also this was breaking backwards compatibility as if the
   focused window is covered by a modal one, the focused window was not
   reporeted and this was putting the active window in a bad state as
   the latter is either the focused window or the one the user is touching.

2. Window change events are too frequent as on window transition things
   are chanign a lot. Now we are trottling the windows changed events
   at the standard recurring accessibility event interval.

3. Fixed a wrong flag comparison and removed some unneded code.

buy:15434666
bug:15432989

Change-Id: I825b33067e8cbf26396a4d38642bde4907b6427a