Fix unable to drag notification to enter split screen

Fix exception when resetting adjacent launch root, dragging expandable
notification and logging unknown activity dragging event.

Fix: 202276040
Fix: 197968594
Fix: 204900540
Test: tests passed
Test: drag expandable notification to split won't fail
Change-Id: I4bb6c361df2034547079a6e9d932b0f5589b3e35