Restore HeadsetClientStateMachine.getCurrentAgFeatures() reporting of...

Restore HeadsetClientStateMachine.getCurrentAgFeatures() reporting of EXTRA_AG_FEATURE_VOICE_RECOGNITION.

Reporting appears to have been disabled during a refactor on 2017-01-20 in commit 97f0e92a. Other functionality has since been restored (e.g. HeadsetClientService.startVoiceRecognition()), so this omission appears to be an oversight.

Bug: 75962618
Test: make, atest BluetoothInstrumentationTests, local verification with Pixel 2
Change-Id: I96441cb31c15574df1282a8f87546e821b5a1566