Give mods & resource packs the ability to add seasonal textures/models

[mosharky]

Overview

Some environmental blocks aren't affected by seasons since they aren't affected by biome colours, so I think giving mod and resource pack devs the ability to optionally add per-season textures/models would be great. A season's model could be defined in the blockstates json or something?

Why would this feature be useful?

Even with just Serene Seasons installed, flowers are not affected by biome colours, so it would be great to finally be able to change them. This could allow for more visual clarity when a crop or flower is out of season.