Update 84x246mm guns with weight, volume, and longest_side, addition of M3E1

[feinorgh]

Summary

SUMMARY: Content "Update 84mm launchers with weight, volume, and longest side"

Purpose of change

Contribute to #37374 and #41691.

Putting Sweden into the thick of the apocalypse.

Describe the solution

Update the JSON file with the calculated values, from the method described in #37374

Describe alternatives you've considered

Hrrmphf.

Testing

Test suite passes, JSON validates, the guns are spawnable and usable in-game.

Additional context

M3 recoilless rifle

The M3 is the version of the Carl-Gustaf from the 90:s, still in use in the US as the M3 MAAWS. I updated the values for the actual M3 version, which does not have rails and accessory points like the M3E1 (actually, M4) below.

I calculated the volume for this weapon (and the M3E1) by taking two measurements, one for the full weapon including furniture, and one for just the tube shape. I then calculated the "core" volume through the weapon, based on the width of the furniture (estimated around 35 mm for the handles, sight, and the shoulder rest).

I then calculated the volume of the tube as a regular cylinder based on its width and height. Calculating the volume of the section through the tube based on the core width, I subtracted this value from the cylinder volume, and then added the result to the "core" volume. This should give a reasonable estimate of the full volume of the weapon.

Spreadsheet values:
https://docs.google.com/spreadsheets/d/10TeuTTjwusbWB9SaH-nq03bMWDyILylU9Btvtu3uTDM/edit#gid=93328453&range=A98

Calculation:
https://docs.google.com/spreadsheets/d/10TeuTTjwusbWB9SaH-nq03bMWDyILylU9Btvtu3uTDM/edit#gid=835787504&range=A132

M3E1 (M4)

This is the modern version of the Carl-Gustaf (from 2014 and onward). This seemed to be the version that was included in the game before (but with the wrong name). I made a new entry for this weapon, updated the description, and added the weapon to the itemgroup lists with similar values as the M3.

The volume calculation was done in the same manner as for the M3.

Calculation
https://docs.google.com/spreadsheets/d/10TeuTTjwusbWB9SaH-nq03bMWDyILylU9Btvtu3uTDM/edit#gid=835787504&range=X133

AT4

This is mostly just a tube. I calculated the average "height" of the tube by taking the area and dividing it with the length of the weapon, and then calculated the volume of this as a cylinder.

https://docs.google.com/spreadsheets/d/10TeuTTjwusbWB9SaH-nq03bMWDyILylU9Btvtu3uTDM/edit#gid=93328453&range=A17