Merge "Changing BluetoothHeadset APIs from @hide to @SystemApi" into stage-aosp-master am: 913ea0a167

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/15728282

Change-Id: Ie0c79a9d5ae7873f21676ce1c615ee41a22fa394