LeAudio: Introduce capabilities struct

This formalizes the audio capabilties and how they are derived from
the LTVs. This patch unifies the approach to parsing capabilities
LTVs with the configuration LTVs.

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: I575510a18df895e93063f2bc414d79bbc7a4f5b9