Add RootTargetPreparer for explicitly specifying the root dependency am: 4cc54592 am: 7d585b71

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/native/+/26804795



Change-Id: I9323261c0bbc49731f8c9d3f4c8da1dad84ec1c4
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>