Merge "Correct HeadsetMediaButton behavior for external calls." into tm-dev am: a1367aa0ff am: 61faebf651

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/services/Telecomm/+/17325507

Change-Id: Iebbccaf04ec3384b5a9402c8fb6aadd67ee072e6