Include the local state obj in ACTION_DRAG_STARTED events

Fixes bug 3362502

The underlying cause was that the DragEvent.obtain() variant which
clones an existing event was failing to copy the local state field.

This change also moves the logic for inserting the local state object
into DragEvents about to be dispatched from the Binder incall thread
into the main-thread code sequence.  This is to eliminate any potential
SMP memory coherency issues around drag start vs incoming events
needing to refer to the local state object.

Change-Id: I368e8936dbf8a00b7d5cc19c2ef0101bd75b6b2d