Add flag for immunity to skin irritants

[zachary-kaelan]

Summary

Infrastructure "Add IRRITANT_IMMUNE flag for describing immunity to skin irritants"

Purpose of change

When setting up an effect condition, I noted a significant number of potential mutations and mutation armors, and a few different armor suits, that could all reasonably provide total protection of the skin from irritating substances. The list in the effect condition was getting really long.

Describe the solution

Create a new flag, IRRITANT_IMMUNE, and add it to anything that seems like it would either prevent irritating substances from making contact with the skin. or just remove the skin entirely. I based it on coverage, existing flags, and descriptions.

Describe alternatives you've considered

Use the ACID_IMMUNE flag instead. While a heavy coat of stiff fur would reasonably prevent a spray of itch powder from making contact with the skin, acid would burn straight through.

Use the WATERPROOF and/or RAINPROOF flags instead. While letting a few droplets of water slip between your glove and arm sleeves isn't worth fussing about (it will just evaporate), any amount of itching powder slipping through would suck, and it would find its way over a lot of the rest of your body as you're swinging weapons and ducking and weaving and such.

Testing

The JSON style checker will yell at me if something is goofed.

Additional context

This is just for "all-or-nothing" things that cover basically all the skin on the body. More nuanced calculations will presumably come in #72271.

[Maleclypse]

OK I still have some questions about some of these like patch skin and lupine fur but overall I think this makes sense.