HFPClient: Support HF Indicators

* Update HFP 1.7 HAL info in HeadsetClientHalConstants.java
* Add send BIEV entry
* Listen ACTION_BATTERY_CHANGED to update battery level
* Send initial battery level
* Add corresponding tests

Tag: #feature
Test: atest BluetoothInstrumentationTests
Bug: 176275446
Change-Id: Id0df4ffbca57463d3b5712d11e399b6094896d18