leaudio: Add BAP Broadcaster implementation

This implements the single-instance Broadcaster entity
for creating, configuring and managing audio broadcasts.
Each registered broadcast is an independently controlled
state machine, which can be started, stopped, suspended or
destroyed. The implementation takes care of all the
advertising, ISO channel creation and audio data routing

Note, that currently all the system audio is trasfered over
the broadcast stream including all the sonification events
like clicks and notifications. Current audio session client
implementation is designed to work with either unicast or
broadcast, but not both at the same time.

Bug: 150670922
Tag: #feature
Test: atest BluetoothInstrumentationTests bluetooth_test_broadcaster bluetooth_test_broadcaster_sm bluetooth_le_audio_test
Sponsor: jpawlowski@
Change-Id: I4e9c95d4b6a4fe0a7911bb8702ee7f41ff500470