Add split support for 3P launcher

* Copied logic mostly from
Base/RecentsViewStateController
* There's one KI crash specific to 3P
(b/209694087)
* Swipe to home animation is TODO, but
then again it also seems incorrect for
full-screen app. 3P has many cosmetic issues
throughout.

Bug: 195607777
Test: Tested w/ Nova launcher with grid
and non-grid, able to invoke split screen with
same animations as 1P launcher

Change-Id: I35a1bc92a51caccac4214289e614000cd47bb503