broadcaster: Refactor handling broadcast ID

This patch is another step to properly align the Java API
with the native layer implementation.

This change makes use of the broadcast ID in the native
layer API in place of the vague instance ID, to seamlesly
match the Java API and simplify the native layer API and avoid
any translations between the two. Previously used instance ID
(after the advertising instance identifier) is now only used
when talking to the advertiser module but is no longer exposed
to the upper layers, where only broadcast ID exists.

This also fixes the following error that was caused by the broadcast
ID being not yet known to the Java layer at the time broadcast is created:
  LeAudioService  D  Broadcast Instance id: 15740086 paused.
  LeAudioService  E  Unknown Broadcast ID for broadcast instance: 15740086

Bug: 150670922
Tag: #feature
Test: atest BluetoothInstrumentationTests bluetooth_test_broadcaster_sm bluetooth_test_broadcaster
Sponsor: jpawlowski@
Change-Id: Ie524da6fd560bc20ed1eab4fea5035cedbe18f5c