Add RootTargetPreparer for explicitly specifying the root dependency am: 6d6cd37cd7 am: e190b45d2b

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/native/+/26789419

Change-Id: I638cdb601f313a60f42d08d55cc3dd9569c7f6b5
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>