Made Bluetooth codec configuration APIs public.

Continuation of the work started in Android T of making
Bluetooth codec configuration available via public APIs.

BluetoothA2dp#setCodecConfigPreference, BluetoothA2dp#
getCodecStatus & BluetoothA2dp#ACTION_CODEC_CONFIG_CHANGED
are made public instead of system APIs.
setCodecConfigPreference requires a CDM association between
the calling application and the Bluetooth device.

Bug: 170678351
Tag: #feature
Test: atest FrameworkBluetoothTests
Change-Id: I40597060127cf2499548d1906d3d5743f157e131