Tubby Cow: better clothing coverage for bovines, via filters

[kbsmilk]

[MUTANTRACE] [CLOTHING]

About the PR

• Adds filters for 6 different clothing slots, that generally improve clothes' fitting and appearance on the unique bovine shape.
• Affects: jumpsuits, oversuits, belts, satchels, backpacks, and gloves. Only for bovines. Only in the east/west directions.
• Adds a simple base mutantrace proc that is called by update_icon()'s sub-procs. It's helpful for applying filters to clothes based on the mob's mutantrace. The proc does nothing by default.
• There's a custom mutant emote (*udder), for users to toggle the filters on/off.
• Renames a few instances of /obj/effect/distort to /obj/effect/rt; removes its default icon.

Why's this needed?

Cows have clipping issues with nearly every clothing in the game. See this comparison image.
I might suggest testmerging before a full merge, given the wide variety of clothes in game. It's hard testing all these!

Changelog

(u)Smilg
(*)Bovine clothing now fits better, using distortion maps. Please report any clothes combos that look really bad.

[pali6]

With this many filters and things in vis_contents I do worry how this will affect client performance.

[imawxome]

These look really good!

[pali6]

What we could maybe do at some point later (if we care about client performance) is to make a proc that applies a distortion map onto an icon producing a modified icon. This would be a somewhat expensive operation but could be cached and it would remove the potential clientside impact of the many vis_contents things and filters.

[kbsmilk]

oooh that does sound fun. For now though, cows seem to be a really rare mutantrace, so while the filter count is high even for me, it shouldn't be a big impact. All this stuff adds up over time though, so if we get a proc like that, I'd make use of it.

[AXLFAN2000]

absolutely LOVING how this is looking ingame!