Accessibility HOVER_ENTER / EXIT without enclosing EXPLORATION_GESTURE_START / END

1. The initial implementation was not sending the gesture start and end
   events until the the user has moved more than a given slop and did not
   do it faster than a given velocity. However, there is the case where
   if the user did not move or just taped on the screen an exploration
   occurs. The system was not sending the exploration start and end
   events for the latter case.

2. The delaued command for long press was not canceled when the pointer
   moves more than the slop distance.

bug:7282811

Change-Id: I7d98470cd4d9ea9b2519326e5e550ff68b040747