Change BluetoothAudioHalVersion from enum to class

Bug: 315983648
Bug: 307291692
Bug: 307595549
Test: m
Test: atest bluetooth_audio_hal_version_test (with flag on/off)
Test: Bluetooth audio functionality with flag on/off on Pixel
Test: lunch aosp_arm64-trunk_staging-eng; m
Change-Id: I18b639463e19e649f9d82b35e2a6003b9e7d35a2