Merge "Add TabletopModeController in WMShell" into tm-qpr-dev am: fb933d46 am: 3c7723fc

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/21695383



Change-Id: I15ca6d6661552c626f812f3ebd0446a0957b4804
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>