LeAudio: Stream configuration improvements

 - document struct members
 - remove unused `is_active` member
 - reduce utility functions dependency by passing only the
   necessary internal `stream_configuration.stream_params`
   member

Bug: 295972694
Test: atest --host bluetooth_le_audio_test bluetooth_le_audio_client_test bluetooth_test_broadcaster bluetooth_test_broadcaster_state_machine bluetooth_le_audio_codec_manager_test
Change-Id: Ic225eb3fa7b11a36432fa3f2860aaabfbef2b4e5