TouchExplorer long press not working and activation tap not respecting distance slop.

1. The first problem is manifested on Prime. Apparently the Prime screen driver
   is very aggresive in filtering move events that origin from almost the same
   location. Hence, the framework doesn't see a constant stream of events. However,
   the TouchExplorer implementation was assuming a constant event stream to detect
   long press. Refactored the code such that no assumptions for the event stream
   are made.

2. Touch exploring an item and then tapping far away from that item was activating
   it, hence not respecting the distance slop. This was due to incorrect check of
   the latter.

bug:5070917

Change-Id: I3627a2feeb3712133f58f8f8f1ab7a2ec50cdc9a