Fixes the healthdoll not showing robot limbs, or updating when pain goes away. (#22190)

Adds some signals to update the HUD when necessary.

The only one which will fire every tick is in remove_pain, which will
now only fire if there is pain to remove.

The extra update in robotize is necessary because robotize is called
after Initialize, so robot limbs were being set to the wrong colour.

Fixes: #22186

code/modules/organs/organ_external.dm

@@ -510,7 +510,8 @@
 	update_damages()
 	if(owner)
 		owner.updatehealth() //droplimb will call updatehealth() again if it does end up being called
-	update_icon()
+	if (update_icon())
+		SEND_SIGNAL(src, COMSIG_UPDATE_LIMB_IMAGE)
 
 	return created_wound
 
@@ -1357,6 +1358,7 @@ Note that amputating the affected organ does in fact remove the infection from t
 			burn_mod = R.burn_mod
 			robotize_type = company
 			augment_limit += 1	//robotic limbs get one extra augment capacity
+			SEND_SIGNAL(src, COMSIG_UPDATE_LIMB_IMAGE)
 
 	dislocated = -1 //TODO, make robotic limbs a separate type, remove snowflake
 	limb_flags &= ~ORGAN_CAN_BREAK
@@ -1707,6 +1709,7 @@ Note that amputating the affected organ does in fact remove the infection from t
 		return
 	var/last_pain = pain
 	pain = max(0, min(species.total_health * 2, pain - amount))
+	SEND_SIGNAL(src, COMSIG_UPDATE_LIMB_IMAGE)
 	return -(pain-last_pain)
 
 /obj/item/organ/external/proc/add_pain(var/amount)