Text handles movement improvements.

Bug 3329346

Making sure the cursor is never hidden by the finger. Some
vertical movement is not repercuted on the handles' position
if it moves the finger closer to its 'ideal' touch position,
where both the insertion line and the top of the handle are
visible.

Also removed the hysteresis line filter which is not that
usefull and feels sluggy.

Change-Id: I6ad0fed0cf66753c6571b3bc620b1a0f2397c7b2