Fix gesture detection algorithm

This change also
  * Introduces adaptive gesture detecting threshold for time domain in addition to length domain.
  * Tunes the parameters for detecting gesture after fast typing.
  * Fixes a bug in dismissing gesture floating preview text.
  * Cleanup debug messages

Bug: 7218902
Change-Id: Iafccd872c6efe0c3b5ae65fa40b04c80d9f139c7