Kills /obj/shapeshift_holder, replaces it with /datum/status_effect/shapechange_mob, also does a lot of Wabbajack refactoring (#69091)

About The Pull Request

    Deletes /obj/shapeshift_holder, replaces it with /datum/status_effect/shapechange_mob
    Refactors Heretic worm form into a shapeshift spell
    Refactors Wabbajack, and associated code

Fixes #69117
Fixes #65653
Fixes #59127
Fixes #52786
Why It's Good For The Game

/obj/shapeshift_holder was one of the worst remaining abuses of /obj direct subtypes, so I replaced it with a cool fancy datum.

This also decouples the shapeshifting behavior entirely from the shapeshifting spell. So we have support for shapeshifted mobs not sourced from a spell. Which is neat, we could technically swap Wabbajack to use this in the future.
Changelog

cl Melbert
fix: Wabbajacking a shapeshifted mob no longer runtimes horribly. When a shapeshifted mob is wabbajacked, they'll now be removed from their shapeshift and stunned.
fix: Transforming via a shapeshift should no longer rob you of your hearing / runechat awareness.
fix: Shapeshifting plays nicer with holoparasites.
fix: Being polymorphed from a xeno to a non-xeno correctly makes you a non-xeno
refactor: Refactored shapeshifting, the shapeshift holder is now a status effect instead of an object.
refactor: Heretic worm form is a shapeshift spell now, this might have some minor behavioral changes but should overall be the same.
refactor: Refactored Wabbajack (+ cursed pool). Overall a bit more clean / consistent behavior.
/cl

code/modules/mining/lavaland/tendril_loot.dm

@@ -168,7 +168,7 @@
 /obj/item/clothing/neck/necklace/memento_mori/proc/check_health(mob/living/source)
 	SIGNAL_HANDLER
 
-	var/list/guardians = source.hasparasites()
+	var/list/guardians = source.get_all_linked_holoparasites()
 	if(!length(guardians))
 		return
 	if(source.health <= HEALTH_THRESHOLD_DEAD)