Add View.startDragAndDrop and deprecate View.startDrag

This in preparation to adding a new method to cancel an
ongoing drag. This method cannot be called cancelDrag,
stopDrag or endDrag because these names are already
taken by View-derived classes in the framework or in
important apps.

Change-Id: Ie21a778c3253b2d526c0c1bcc423c374ca70ee01