Merge "Make BluetoothHeadsetClient and associated functions @SystemApi" am: e70578157d am: 881867d5e1 am: ab0e7cd2cf am: f15afa4672

Original change: https://android-review.googlesource.com/c/platform/frameworks/base/+/1954516

Change-Id: Ifd0453f1c20b73a218dd84789cecd3779d897b67