Hook up split-launch to legacy transition system

Part 1 of hooking up stage-split to legacy stuff. This
actually routes the legacy remoteAnimation through shell
in order to gather the dividerbar and interract with the
WindowProcessController

Bug: 192279476
Test: atest WindowOrganizerTests.
      use SPLIT_SELECT to launch 2 apps in split and observe.
Change-Id: I4f8802e6eb33f068fae0e4b3c12942bea76e332b