TGMC Ammo HUD Port

Ports over TGMC's Ammo HUD and all relevant code, adapted to work for Polaris's guns. This took me several days, but hey, I learned a bunch. <:
Time to port Aim Mode + Mentorhelp. :3c 
- All guns now have an ammo HUD sprite. If one lacks one, it will be ??? or blank, at which point, make an issue report, as all guns should be working by now.
- Guns will display how many rounds they have left until ammunition runs dry.
- Ammo will only count the casings that CURRENTLY have a projectile in them. This is slightly unrealistic, yes, but it is better and more intuitive for the player. This also enables guns like the revolver to work, given they recycle casings.
- Up to 4 ammo HUDs can be displayed at once, but given we lack TGMC's attachments and guncode, you'll only ever usually see 2. TBD on porting over TGMC guncode. <:
- Ammunition for multiple guns has different colors in the HUD based on what you currently have loaded.
- If you're looking at this later on to add new things. DON'T USE _FLASH IN THE HUD_STATE_EMPTY. THE _FLASH IS ADDED ON BY CODE.
- Grenades have a hud_state, pending us ever porting over a grenade launcher. Rockets ALSO have a hud_state.


Example of Laser/Energy Weapons:
https://i.imgur.com/MGvqGxh.mp4
Captain's Gun:
https://i.imgur.com/Wd0SS3C.gif

Full Test of all weapons:
https://streamable.com/usp4dy

Upstream port of https://github.com/CHOMPStation2/CHOMPStation2/pull/4033

code/modules/projectiles/guns/projectile/shotgun.dm

@@ -1,3 +1,7 @@
+/*
+ * Shotgun
+ */
+
 /obj/item/weapon/gun/projectile/shotgun/pump
 	name = "shotgun"
 	desc = "The mass-produced MarsTech Meteor 29 shotgun is a favourite of police and security forces on many worlds. Uses 12g rounds."
@@ -39,12 +43,14 @@
 		else
 			chambered.loc = get_turf(src) // Eject casing
 		chambered = null
+		M.hud_used.update_ammo_hud(M, src) // TGMC Ammo HUD Port
 
 	// Load next shell
 	if(loaded.len)
 		var/obj/item/ammo_casing/AC = loaded[1] // load next casing.
 		loaded -= AC // Remove casing from loaded list.
 		chambered = AC
+		M.hud_used.update_ammo_hud(M, src) // TGMC Ammo HUD Port
 
 	if(pump_animation) // This affects all bolt action and shotguns.
 		flick("[pump_animation]", src) // This plays any pumping
@@ -125,6 +131,7 @@
 			burst = 2
 			user.visible_message("<span class='danger'>The shotgun goes off!</span>", "<span class='danger'>The shotgun goes off in your face!</span>")
 			Fire_userless(user)
+			user.hud_used.update_ammo_hud(user, src) // TGMC Ammo HUD Port
 			burst = burstsetting
 			return
 		if(do_after(user, 30))	//SHIT IS STEALTHY EYYYYY