Implementation of Bluetooth Audio HAL interface v2

This is the default implementation of Bluetooth Audio Hal v2, and 3
providers are defined.

* BluetoothAudioProvider is the default provider, which is a stub when
  no SessionType matched.
* A2dpSoftwareAudioProvider uses to replace the old A2DP legacy module
  and uses IPC via HIDL interface between Bluetooth stack and Audio HAL.
* HearingAidAudioProvider uses to replace the Hearing Aids module which
  uses UNIX socket as IPC and now there is HIDL based interface.

There is also a shared library named "libbluetooth_audio_session.so" to
provide the linkage directly between this HIDL and its HAL module,
bluetooth_audio. With this library, we can break the library dependency
and guarantee those symbols of libraries while compiling.

Bug: 111519504
Bug: 122503379
Test: boot and manual test

Change-Id: I54d86291482b7fb041a3ac3e171b68a4ed7bfa07