Add assign reader for damage instances, deprecate legacy damage code

[anothersimulacrum]

Summary

SUMMARY: Infrastructure "Add damage instance assign reader, unify item damage loading code"

Purpose of change

This makes it easier to modify the damage type of ranged weapons (instead of all of them dealing DT_STAB, as well as enabling obsoleting legacy members for armor penetration and proportional damage in favor of having one damage object that defines that.

In the future, this will make it easier to allow using damage objects everywhere we have damage, instead of raw integers for various types (in places like item melee damage).

Describe the solution

Add an assign reader for damage_instances and three static functions to validate the assigned damage, and to assign damage using relative and proportional.

Add unconditional_ res_mult and damage_mult to replace proportional damage and add proportional piercing capability, for arrows.

Describe alternatives you've considered

Not doing the JSON changes in the same PR. I probably will back them out and do them in a separate PR later.

Testing

Tests run correctly.

TODO:

• Ensure that damage for things are unchanged with and without this applied
• Make sure this displays correctly
• Make sure that the obsoleted members/new members of damage units all work properly and are slotted in where they should be.

Additional context

Working towards obsoleting use of raw floats over multiple members to assign damage.
Originally started as a look into making a DT_BULLET, and then looking into using damage objects for bullet/gun damage.

[ZhilkinSerg]

I suggest we jsonize damage types too. I actually started this in https://github.com/ZhilkinSerg/Cataclysm-DDA/tree/jsonize-damage-type.

[anothersimulacrum]

Okay, after fixing two issues regarding copy-from, I think everything's working right and this is ready for merge. I've decided to pull out the JSON changes (barring one to prevent load error) to make extra sure that this works with no data migration.

I'll open another PR with those.

[ZhilkinSerg]

Can you resolve conflicts please?

[anothersimulacrum]

Hhm, rebased, but found a bug. Looking into it.

[anothersimulacrum]

Should be good now.