Editor: enable double tap for selection after cut/copy.

* detect double tap in the TextView and pass it to Editor.
* add a timer (with getDoubleTapTimeout) for executing the
  single tap job in Editor.
* if double tap is detected then cancel the single tap job.

This way one tap shows the toolbar if within the timeframe
and two taps select the word and show the toolbar.

Bug: 20442587
Change-Id: I0a117939c896fcb13669346e30c9c48d319576dd