GestureConverter: send HOVER_ENTER and _EXIT events

Previously these were being put in by InputDispatcher automatically, but
ideally it wouldn't have to — an input mapper should produce a
consistent event stream in the first place.

Bug: 317183325
Test: atest inputflinger_tests
Test: with log.tag.InputDispatcherInboundEvent sysprop set to DEBUG,
      manually check events logged to InputDispatcher logcat tag
Change-Id: Ia74c4865da62520c8f8b7484def8b39c3eee820e