Fix issue with drags sometimes not being handled in tests

- ACTION_DRAG_ENTERED does not actually have location data, and
  ACTION_DRAG_LOCATION may not always be sent, which results in no
  target being computed prior to the DROP.  Since the DROP event
  also has location data, we should update in that case as well.

Bug: 234653212
Test: atest TaplTestsTaskbar
Change-Id: I1f7657a95a4f124d98fc0da78b8a3ac2237f91f6