Change the task layout to better match mocks, add "in" animation

This only adds an animation when transitioning into recents. "Out"
animations will come later as they need to be run in parallel with
launching the activity not to introduce any latency.

Test: Open recents on sw600dp device, check recents layout/animations
Bug: 32101881
Change-Id: I367f8e5c106cd06d2a7833c165ecb960a7821ed9