1. Added an Input Filter that interprets the touch screen motion
events to perfrom accessibility exploration. One finger explores.
Tapping within a given time and distance slop on the last exlopred
location does click and long press, respectively. Two fingers close
and in the same diretion drag. Multiple finglers or two fingers in
different directions or two fingers too far away are delegated to
the view hierarchy. Non moving fingers "accidentally grabbed the
device for the scrren" are ignored.
2. Added accessibility events for hover enter, hover exit, touch
exoloration gesture start, and end. Accessibility hover events
are fired by the hover pipeline. An accessibility event is
dispatched up the view tree and the topmost view fires it.
Thus predecessors can augment the fired event. An accessibility
event has several records and a predecessor can optionally
modify, delete, and add such to the event.
3. Added onPopulateAccessibilityEvent and refactored the existing
accessibility code to use it.
4. Added API for querying the currently enabled accessibility services
by feedback type.
Change-Id: Iec03c6c3fe298de3f14cb6efdbb9b198cd531a0c
ac84d3ba81