Adds HEAP for the F903 [ADMIN-SPAWN ONLY] (cmss13-devs#4389)

# About the pull request

Adds HEAP magazines to the TWE. They are admin-spawned. Does NOT spawn
with the ERT
Tested locally.

# Explain why it's good for the game

Why the hell does the TWE not have HEAP?


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

Put screenshots and videos here with an empty line between the
screenshots and the `<details>` tags.

</details>


# Changelog
:cl:
add: Added HEAP F903 magazines. Does NOT spawn with the ERT presets.
ADMIN SPAWN ONLY.
imageadd: Added F903 ammo band icons.
/:cl:

code/modules/projectiles/magazines/rifles.dm

@@ -471,8 +471,8 @@
 	default_ammo = /datum/ammo/bullet/rifle
 	max_rounds = 30
 	gun_type = /obj/item/weapon/gun/rifle/rmc_f90
-	ammo_band_icon = "+m41a_band"
-	ammo_band_icon_empty = "+m41a_band_e"
+	ammo_band_icon = "+aug_band"
+	ammo_band_icon_empty = "+aug_band_e"
 
 /obj/item/ammo_magazine/rifle/rmc_f90/marksman
 	name = "\improper F903A1 Marksman magazine (10x24mm)"
@@ -483,3 +483,19 @@
 	gun_type = /obj/item/weapon/gun/rifle/rmc_f90/scope
 	max_rounds = 20
 	ammo_band_color = AMMO_BAND_COLOR_AP
+	ammo_band_icon = "+aug_dmr_band"
+	ammo_band_icon_empty = "+aug_dmr_band_e"
+
+/obj/item/ammo_magazine/rifle/rmc_f90/heap
+	name = "\improper F903 HEAP magazine (10x24mm)"
+	desc = "A 10mm armor piercing high explosive assault rifle magazine used by the royal marines."
+	default_ammo = /datum/ammo/bullet/rifle/heap
+	ammo_band_color = AMMO_BAND_COLOR_HEAP
+
+/obj/item/ammo_magazine/rifle/rmc_f90/marksman/heap
+	name = "\improper F903A1 Marksman magazine (10x24mm)"
+	desc = "A 10mm armor piercing high explosive assault rifle magazine used by the royal marines."
+	icon_state = "aug_dmr"
+	item_state = "aug_dmr"
+	default_ammo = /datum/ammo/bullet/rifle/heap
+	ammo_band_color = AMMO_BAND_COLOR_HEAP