Merge "Wait for shell drop target to be ready for handling drags in tests" into udc-dev am: 52cc03e42c am: d03767df3d am: f55cbe1374 am: a1f3bd39d1

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/Launcher3/+/22935091

Change-Id: I49b63d4c438a4dd85bb21a314ca69c7eef2dec32
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>