Merge "Changing BluetoothHeadset APIs from @hide to @SystemApi" into stage-aosp-master am: 913ea0a167 am: 41dc0fb942

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

Change-Id: I107305bf077055f0b210a2ad4c00ab13610c567b