Alternate Appearance system (from tgstation/-tg-station#16586)

This adds an "alternate appearance system" using image overrides and a new
handler system.

Usage:
 - Create a new `image()` casted as `var/image`
 - Set image.override = 1
 - Call mob.add_alt_appearance("appearance_ID", image, listOfMobsToDisplayTo).
 - To remove an image, you use mob.remove_alt_appearance("appearance_ID")

Comes with one usage, cardborg costumes. They will now disguise you as a
standard borg to any silicon mobs and yourself.
As this is a per-client system, that means that only silicon mobs and you will
see yourself as a standard borg. All other mobs will see you as a silly
human in a cardborg costume.

code/modules/clothing/head/misc.dm

@@ -89,14 +89,6 @@
 	item_state = "greenbandana"
 	flags_inv = 0
 
-/obj/item/clothing/head/cardborg
-	name = "cardborg helmet"
-	desc = "A helmet made out of a box."
-	icon_state = "cardborg_h"
-	item_state = "cardborg_h"
-	flags = HEADCOVERSEYES | HEADCOVERSMOUTH
-	flags_inv = HIDEMASK|HIDEEARS|HIDEEYES|HIDEFACE
-
 /obj/item/clothing/head/justice
 	name = "justice hat"
 	desc = "Fight for what's righteous!"

code/modules/clothing/head/misc_special.dm

@@ -5,7 +5,7 @@
  *		Ushanka
  *		Pumpkin head
  *		Kitty ears
- *
+ *		Cardborg Disguise
  */
 
 /*
@@ -207,4 +207,24 @@
 	var/icon/earbit = new/icon("icon" = 'icons/mob/head.dmi', "icon_state" = "mouseyinner")
 	mob.Blend(earbit, ICON_OVERLAY)
 
-	icon_override = mob
+	icon_override = mob
+
+/obj/item/clothing/head/cardborg
+	name = "cardborg helmet"
+	desc = "A helmet made out of a box."
+	icon_state = "cardborg_h"
+	item_state = "cardborg_h"
+	flags = HEADCOVERSEYES | HEADCOVERSMOUTH
+	flags_inv = HIDEMASK|HIDEEARS|HIDEEYES|HIDEFACE
+
+/obj/item/clothing/head/cardborg/equipped(mob/living/user, slot)
+	..()
+	if(ishuman(user) && slot == slot_head)
+		var/mob/living/carbon/human/H = user
+		if(istype(H.wear_suit, /obj/item/clothing/suit/cardborg))
+			var/obj/item/clothing/suit/cardborg/CB = H.wear_suit
+			CB.disguise(user, src)
+
+/obj/item/clothing/head/cardborg/dropped(mob/living/user)
+	..()
+	user.remove_alt_appearance("standard_borg_disguise")

code/modules/clothing/suits/miscellaneous.dm

@@ -199,6 +199,26 @@
 	body_parts_covered = UPPER_TORSO|LOWER_TORSO
 	flags_inv = HIDEJUMPSUIT
 
+/obj/item/clothing/suit/cardborg/equipped(mob/living/user, slot)
+	..()
+	if(slot == slot_wear_suit)
+		disguise(user)
+
+/obj/item/clothing/suit/cardborg/dropped(mob/living/user)
+	..()
+	user.remove_alt_appearance("standard_borg_disguise")
+
+/obj/item/clothing/suit/cardborg/proc/disguise(mob/living/carbon/human/H, obj/item/clothing/head/cardborg/borghead)
+	if(istype(H))
+		if(!borghead)
+			borghead = H.head
+		if(istype(borghead, /obj/item/clothing/head/cardborg)) //why is this done this way? because equipped() is called BEFORE THE ITEM IS IN THE SLOT WHYYYY
+			var/image/I = image(icon = 'icons/mob/robots.dmi' , icon_state = "robot", loc = H)
+			I.override = 1
+			I.overlays += image(icon = 'icons/mob/robots.dmi' , icon_state = "eyes-robot") //gotta look realistic
+			H.add_alt_appearance("standard_borg_disguise", I, silicon_mob_list+H) //you look like a robot to robots! (including yourself because you're totally a robot)
+
+
 /obj/item/clothing/suit/poncho
 	name = "poncho"
 	desc = "Your classic, non-racist poncho."

code/modules/mob/login.dm

@@ -70,6 +70,12 @@
 	//readd this mob's HUDs (antag, med, etc)
 	reload_huds()
 
+	if(viewing_alternate_appearances && viewing_alternate_appearances.len)
+		for(var/aakey in viewing_alternate_appearances)
+			var/datum/alternate_appearance/AA = viewing_alternate_appearances[aakey]
+			if(AA)
+				AA.display_to(list(src))
+
 	CallHook("Login", list("client" = src.client, "mob" = src))
 
 // Calling update_interface() in /mob/Login() causes the Cyborg to immediately be ghosted; because of winget().