Fix: Undo for drag and drop.

Drag and drop operation can be merged with last edit
operation. In this case, insert and delete were recorded as
independent operations even if they were done in one batch
edit.
With this CL, we always create dedicated undo/redo state for
drag and drop.

Bug: 28588666
Bug: 30297308
Bug: 29871372
Change-Id: Ib4cb144c6b9b5aa095bc9208fcdedaa737964126