Refactors the mind.original variable into non reference variables. Improving player mob GC (#17219)

code/datums/ai_laws.dm

@@ -93,7 +93,7 @@
 
 
 /mob/living/silicon/proc/sync_zeroth(datum/ai_law/zeroth_law, datum/ai_law/zeroth_law_borg)
-	if(!is_special_character(src) || mind.original != src)
+	if(!is_special_character(src) || !mind.is_original_mob(src))
 		if(zeroth_law_borg)
 			laws.set_zeroth_law(zeroth_law_borg.law)
 		else if(zeroth_law)

code/datums/mind.dm

@@ -23,7 +23,10 @@
 	var/key
 	var/name				//replaces mob/var/original_name
 	var/mob/living/current
-	var/mob/living/original	//TODO: remove.not used in any meaningful way ~Carn. First I'll need to tweak the way silicon-mobs handle minds.
+	/// The original mob's UID. Used for example to see if a silicon with antag status is actually malf. Or just an antag put in a borg
+	var/original_mob_UID
+	/// The original mob's name. Used in Dchat messages
+	var/original_mob_name
 	var/active = 0
 
 	var/memory
@@ -82,9 +85,15 @@
 				qdel(i)
 		antag_datums = null
 	current = null
-	original = null
 	return ..()
 
+/datum/mind/proc/set_original_mob(mob/original)
+	original_mob_name = original.real_name
+	original_mob_UID = original.UID()
+
+/datum/mind/proc/is_original_mob(mob/M)
+	return original_mob_UID == M.UID()
+
 /datum/mind/proc/get_display_key()
 	var/clientKey = current?.client?.get_display_key()
 	return clientKey ? clientKey : key