Integrate pip to split flow with shell-transition

Integrate moveToStage API with open-to-side shell-transition. Also
sketch exit pip to split transition to merge exit pip and enter split
transitions as one.

Bug: 206487881
Test: atest WMShellUnitTests
Test: moveToSideStage command works with shell-transition
Test: tap "enter split" on PIP window, verified it enters split screen
      as expectedly.
Change-Id: Ibccc08b277a0c38bfb31411cbe5e31941a6bacf1