iron teeth character trait (#6512)

# About the pull request
adds "iron teeth" trait for 1 point that allows marines to hold stuff in
their face slot with no fear of it falling out when they drop
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# Explain why it's good for the game
i tried to larp as rambo and my combat knife fell out of my mouth and i
thought man you can only hold minor shit in your face slot would it be
cool if it was a little more useful so here we are
besides more character traits is good theres a shortage of them i think
# Testing Photographs and Procedure
<details>
<summary>Screenshots & Videos</summary>

got the trait... put a knife in my mouth... rested... hit myself with an
explosion to stun... knife was still in my mouth... no runtimes

</details>


# Changelog
:cl:
add: Adds "Iron teeth" trait.
/:cl:

---------

Co-authored-by: Contrabang <[email protected]>
Co-authored-by: Zonespace <[email protected]>

code/__DEFINES/traits.dm

@@ -233,6 +233,8 @@
 #define TRAIT_IN_TUTORIAL "t_IN_TUTORIAL"
 /// If the mob is cloaked in any form
 #define TRAIT_CLOAKED "t_cloaked"
+/// If the mob won't drop items held in face slot when downed
+#define TRAIT_IRON_TEETH "t_iron_teeth"
 
 // -- ability traits --
 /// Xenos with this trait cannot have plasma transfered to them

code/datums/elements/mouth_drop_item.dm

@@ -18,7 +18,7 @@
 /datum/element/mouth_drop_item/proc/item_equipped(obj/item/I, mob/living/carbon/human/user, slot)
 	SIGNAL_HANDLER
 
-	if(slot == WEAR_FACE)
+	if(slot == WEAR_FACE && !HAS_TRAIT(user, TRAIT_IRON_TEETH))
 		I.RegisterSignal(user, COMSIG_LIVING_SET_BODY_POSITION, TYPE_PROC_REF(/obj/item, drop_to_floor))
 
 /datum/element/mouth_drop_item/proc/item_dropped(obj/item/I, mob/living/carbon/human/user)

code/modules/character_traits/biology_traits.dm

@@ -130,3 +130,17 @@
 /datum/character_trait/biology/hardcore/unapply_trait(mob/living/carbon/human/target)
 	REMOVE_TRAIT(target, TRAIT_HARDCORE, ROUNDSTART_TRAIT)
 	..()
+
+/datum/character_trait/biology/iron_teeth
+	trait_name = "Iron Teeth"
+	trait_desc = "You've got iron teeth or really good dental insurance. Items in your face slot won't fall out when you go down."
+	applyable = TRUE
+	cost = 1
+
+/datum/character_trait/biology/iron_teeth/apply_trait(mob/living/carbon/human/target, datum/equipment_preset/preset)
+	ADD_TRAIT(target, TRAIT_IRON_TEETH, ROUNDSTART_TRAIT)
+	..()
+
+/datum/character_trait/biology/iron_teeth/unapply_trait(mob/living/carbon/human/target)
+	REMOVE_TRAIT(target, TRAIT_IRON_TEETH, ROUNDSTART_TRAIT)
+	..()