Enhance LoopingAudioSource behavior inside ConcatenatingAudioSource

[maknon]

Is your feature request related to a problem? Please describe.
current LoopingAudioSource is just a repeated AudioSource inside the playlist. this causes some strange behavior when the user use seekToNext or seekToPrevious where the user would expect to go to the next LoopingAudioSource in the playlist but this is not the case.

Describe the solution you'd like
LoopingAudioSource to be considered as single AudioSource inside the playlist (ConcatenatingAudioSource) so that seekToNext will jump to the next LoopingAudioSource.

in addition, listening to currentIndexStream shall result with the currentIndex of LoopingAudioSource. sequenceState can have the currentIndex within the LoopingAudioSource itself

Describe alternatives you've considered
nothing so far

Additional context
nothing