[Keyboard][Handwriting] Replace HandwritingPadsManager with HandwritingP...

...adTargetHandler
Let's Change the comment to the following, starting line 66:

The optional steps are "longpress", "newTargetActivate", and "move". They happen respectively when the target is long pressed, the target is pressed while there a new target is about to be activated, or then the touch moves within the target. These events are optional and does not affect the life cycle of the handler.