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/research/xenobiology/crossbreeding/_mobs.dm

@@ -21,7 +21,7 @@ Slimecrossing Mobs
 	/// If TRUE, we self-delete (remove ourselves) the next time we turn back into a human
 	var/remove_on_restore = FALSE
 
-/datum/action/cooldown/spell/shapeshift/slime_form/restore_form(mob/living/shape)
+/datum/action/cooldown/spell/shapeshift/slime_form/do_unshapeshift(mob/living/caster)
 	. = ..()
 	if(!.)
 		return