Adds Helmets + Visor To Synth Vendor | Grey M10 Helmet Addition (#4306)

# About the pull request

Adds several helmet options to the synth vendor (M10, Corpsman and
Technician Helmets), also adds a new 'grey' helmet that can be vended
that is essentially a standard M10 helm but defaulted to the grey/urban
camo. Also adds a riot visor to the vendor.

# Explain why it's good for the game

The helmets are already available to synths across the ship, this just
speeds up the synthetics dressing up time. The grey helmet allows a
synth to match their default synth armour with a helmet no matter the
map.


# Testing Photographs and Procedure
<details>
<summary>Screenshots & Videos</summary>

Grey helmet and visor
![Screenshot 2023-09-02 01 35
54](https://github.com/cmss13-devs/cmss13/assets/6595389/e8b57648-6860-440e-8303-d442fae3fdd8)

Menu
![Screenshot 2023-09-02 01 37
42](https://github.com/cmss13-devs/cmss13/assets/6595389/cca27911-3295-4083-9887-399723f25abf)


</details>


# Changelog
:cl:
add: Synthetic vendors now have the option to vend several helmets and a
riot visor. Including a standard M10 helmet defaulted to non-camo grey.
/:cl:

Co-authored-by: Steelpoint <[email protected]>

code/game/machinery/vending/vendor_types/crew/synthetic.dm

@@ -232,6 +232,12 @@ GLOBAL_LIST_INIT(cm_vending_clothing_synth_snowflake, list(
 	list("MP Cap", 12, /obj/item/clothing/head/beret/marine/mp/mpcap, null, VENDOR_ITEM_REGULAR),
 	list("RO Cap", 12, /obj/item/clothing/head/cmcap/req, null, VENDOR_ITEM_REGULAR),
 	list("Officer Cap", 12, /obj/item/clothing/head/cmcap/ro, null, VENDOR_ITEM_REGULAR),
+	list("Marine Helmet", 12, /obj/item/clothing/head/helmet/marine, null, VENDOR_ITEM_REGULAR),
+	list("Grey Marine Helmet", 12, /obj/item/clothing/head/helmet/marine/grey, null, VENDOR_ITEM_REGULAR),
+	list("Technician Helmet", 12, /obj/item/clothing/head/helmet/marine/tech, null, VENDOR_ITEM_REGULAR),
+	list("Corpsman Helmet", 12, /obj/item/clothing/head/helmet/marine/medic, null, VENDOR_ITEM_REGULAR),
+	list("Attachable Helmet Shield", 12, /obj/item/prop/helmetgarb/riot_shield, null, VENDOR_ITEM_REGULAR),
+
 
 	list("SUIT", 0, null, null, null),
 	list("Bomber Jacket, Brown", 12, /obj/item/clothing/suit/storage/bomber, null, VENDOR_ITEM_REGULAR),

code/modules/clothing/head/helmet.dm

@@ -718,6 +718,12 @@ GLOBAL_LIST_INIT(allowed_helmet_items, list(
 	specialty = "M10 technician"
 	built_in_visors = list(new /obj/item/device/helmet_visor, new /obj/item/device/helmet_visor/welding_visor)
 
+/obj/item/clothing/head/helmet/marine/grey
+	desc = "A standard M10 Pattern Helmet. This one has not had a camouflage pattern applied to it yet. There is a built-in camera on the right side."
+	icon_state = "c_helmet"
+	item_state = "c_helmet"
+	flags_atom = NO_SNOW_TYPE
+
 /obj/item/clothing/head/helmet/marine/tech/tanker
 	name = "\improper M50 tanker helmet"
 	desc = "The lightweight M50 tanker helmet is designed for use by armored crewmen in the USCM. It offers low weight protection, and allows agile movement inside the confines of an armored vehicle. Features a toggleable welding screen for eye protection."