Allow Warm/Temperate/Cold Farm Animal features to be used on any variant

The new farm animal variants added in the latest snapshots for the Spring Drop are really cool, adding some neat texture/model features without drastically changing the mobs. However, despite all of the mobs having an updated texture size, you cannot make use of these new model and texture features on the other variants.

For example, the warm and cold cows both have bigger and slightly different 2x2 horns, but you cannot change the texture on a temperate cow to also use these horn shapes/sizes. Similarly, the cold pigs and cows have a "jacket" layer used for their fur, but you cannot use these features on the temperate or warm variants. And the new cold chicken has a little tail and a "helmet" layer but you can't also use these on a warm or temperate chicken.

I'd initially reported this as a bug (MC-280017) but it was marked as invalid.

I think it would make much more sense (and also be great for resource pack makers!) if the Warm/Temperate/Cold farm animals all shared one model, which would allow resource pack makers to make use of all of these new texture and model features for any of the new mob variants! The new features would just appear on the model based on the texture used, so if its transparent then it just wont render on the model. The cow variants would need a slight texture update to make the texture layouts consistent. As of right now the snout is in slightly different spots because of the location of the cold cow's horn texture.