Adds boss music functionality and gives hierophant it's own thematic fight song! (#77149)

## About The Pull Request

Adds compatibility to the code to assign music to individual mobs that
are played in full length to the player when aggro'd. Music maintains
for the entire length, ends, and is repeated if the mob isn't dead.
Music is instantly stopped if the mob generating it dies. Other coding
avenues were explored around dynamic music generation and allowing for
the music to end more naturally, but they were found to be very buggy or
impossible to code due to dreammaker having a very........... tense
relationship with audio. It also (had to be reminded of this!), lowers
the audio of hierophants attacks to make music more audible.

## Why It's Good For The Game

This has the potential to add so much thematic flavor to mobs and events
in game, it's great! Represents a big step forward in terms of sound
design on tg. Thanks to John Willard for fully coding!
Check out the theme here --> https://youtu.be/mWgv1CHtd4Y

## Changelog

🆑
add: Adds boss music functionality.
sound: Adds hierophants boss track, tweaks hierophant boss noises.
/🆑

---------

Co-authored-by: JohnFulpWillard <53777086+JohnFulpWillard@users.noreply.github.com>

code/datums/looping_sounds/_looping_sound.dm

@@ -52,8 +52,9 @@
 	var/loop_started = FALSE
 	/// If we're using cut_mid, this is the list we cut from
 	var/list/cut_list
-	/// The index of the current song we're playing in the mid_sounds list, only used if in_order is used
-	var/audio_index = 1
+	///The index of the current song we're playing in the mid_sounds list, only used if in_order is used
+	///This is immediately set to 1, so we start the index at 0
+	var/audio_index = 0
 
 	// Args
 	/// Do we skip the starting sounds?