Merge "Add some type annotations, mainly to help the IDE." into main am: 178665e03b

Original change: https://android-review.googlesource.com/c/platform/development/+/2749473

Change-Id: I9c9672d585f4555ecdca43b95fb75ce6fb978f29
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>