Merge "Downmix: Add AIDL placeholder implementation and vts test" am: 1ad0ff0f79 am: a1b3286a15 am: 0ec3ca4666

Original change: https://android-review.googlesource.com/c/platform/hardware/interfaces/+/2309207

Change-Id: I1f531719526cecb88368b42034121d2fac599c47
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>