BluetoothAudio HAL: flip to be enabled by default

Change to new properties + swap audio XML files, and supports following
scenarios:
1) (default) audio_policy_configuration.xml
   Using BluetoothAudio HAL (+ A2DP offload if supported)
2) audio_policy_configuration_a2dp_offload_disabled.xml
   Using BluetoothAudio HAL only when A2DP offload is supported but
   disabled.
3) audio_policy_configuration_bluetooth_legacy_hal.xml
   No BluetoothAudio HAL nor A2DP offload

Bug: 126304229
Test: Switch BluetoothAudio HAL and A2DP offload manully
Change-Id: I6d996d616c6c0b998699f90dbaebb7d70ef3237c
Merged-In: I6d996d616c6c0b998699f90dbaebb7d70ef3237c