Allow split select transition from desktop mode.

Introduces a new controller to manage an app entering split select mode
from desktop mode.

Video: http://recall/-/gjymLwjdDT07aWqaK6101a/gU56zTDcWov6ukbKuH8tFx
Flag: ENABLE_SPLIT_FROM_DESKTOP_TO_WORKSPACE
Bug: 286550932
Bug: 279586624
Test: Manual

Change-Id: Ib94402553c88286894d94c95c38cac125be23a0d