Adds a shotgun choke for the M37A2

[VileBeggar]

About the pull request

adds a new barrel attachment for the m37a2 shotgun. it's available in squad prep and requisitions in small quantities.
it changes the shotgun from a secondary utility weapon to more of a CQC primary, similar-ish to the m39. sprites were done by thwomper.

the stat changes are as follows,
negatives are:

1. reduces the damage output of the shotgun by 30%
2. remove any stunning or slowing ability from slugs/buckshot
3. increases the recoil by 2 steps

positives are:

1. increases the max range of shells by 1 tile
2. doubles the fire rate from 0.5 bullets per second to 1 bullet per second
3. decreases falloff by 30%
4. decreases bonus projectile scatter by 5 (buckshot is now a much tighter formation)
5. increases accuracy by 25%
6. increases bullet velocity by 1 step

it also changes the firing sound to a different one, so enemies can quickly differentiate it from a standard m37. video is slightly outdated

Choker.2.mp4

DPS-wise, it's pretty similar to the MK2.:

• BUCKSHOT: 182 DPS, vs MK2 STANDARD: 176 DPS
• FLECHETTE: 84 DPS, vs MK2 AP: 132 DPS.

it's fairly solid at clearing out soft targets, but flechette rounds lag behind regular AP ammo. i think the risk of being forced to get close up is worth the small increase in damage. note, i am unsure of touching flechette damage values currently due to #8048 being in the air for a testmerge.

some guncode lines were changed to get damage multipliers working for bonus projectiles, along with a new variable that increases the max range of projectiles. PBs now inherit damage multipliers too

Explain why it's good for the game

it's a new, fun way to utilize a primary weapon. the attachments marines currently have are pretty lackluster, with most of them being bland stat increases and some of them just straight up being absolute garbage. hopefully by adding more unique, mechanic-based attachments and tweaking some of the others we can make the system a lot better and fun. i think this attachment is a good start

while the numbers might not be all there yet, they can always be tweaked, and with the lack of stuns/slow i doubt this weapon will be that oppressive against xenos.

Testing Photographs and Procedure

Screenshots & Videos

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

Changelog

🆑 Vile Beggar, thwomper
add: Adds a new shotgun choke attachment to squad prep and requisitions vendors for the M37A2 shotgun.
/:cl:

[BasilHerb]

Looks incredible. I wished all attachments would go down this path. Currently, so many are just stat changes that are stupidly boring, whereas this actually changes the gun completely. Soul author strikes again…

[nauticall]

I'm not sure what the attachment item sprite is supposed to be - if it's the choke, it doesn't look like one. The item sprite should ideally mimic a larger, more detailed version of the attachment's sprite on the weapon, not something from an entirely different perspective or color palette.

didn't see other maintainer request

[thwompa]

I'm not sure what the attachment item sprite is supposed to be - if it's the choke, it doesn't look like one. The item sprite should ideally mimic a larger, more detailed version of the attachment's sprite on the weapon, not something from an entirely different perspective or color palette.

Issue addressed, sprites forwarded to OP.