audio: Add IBluetoothA2dp

Similar to IBluetooth interface which controls SCO/HFP,
IBluetoothA2dp controls the A2DP profile. This interface
replaces the following string parameters:

AUDIO_PARAMETER_A2DP_RECONFIG_SUPPORTED
AUDIO_PARAMETER_RECONFIG_A2DP
"A2dpSuspended"

Also, refactor fields used by Module implementation
for persistent child interfaces.

Bug: 270731693
Test: atest VtsHalAudioCoreTargetTest
Change-Id: Ie62952c3bc3af2f53535d716e5b57bf48c661306
Merged-In: Ie62952c3bc3af2f53535d716e5b57bf48c661306