ClimateSwaps and Terrain in Rainforest

[KABoissonneault]

Re-opening the conversation on winter in Rainforest regions.

https://forums.dfworkshop.net/viewtopic.php?t=3397

In short, classic does not have winter in Rainforest regions, but DFU does. We're in a pretty awkward spot though:

• For archives below 500, we do get winter swaps (ex: walls have snow)
• For ground textures and terrain, we do have snow
• For archives above 500 (vegetation), we do not get winter swaps
  In addition, for the WeatherManager, Rainforest is a snow-free region.

So in regions like Totambu, we have snow-covered ground and buildings, but green vegetation and no snow weather.

The dfworkshop thread leaves the issue undecided.

I believe the solution for DFU should be to match classic, but offer the right tools for modders who want to make use of DF's unused assets to finish the job. DFU's situation diverges from classic but does not offer a good enough implementation to justify it, IMO.

What this means concretely:

• TerrainMaterialProvider.GetClimateInfo should exclude Rainforest WorldClimate in addition to Desert BaseClimate. TerrainMaterialProvider can already be overriden by mods, so it's pretty simple to restore
• ClimateSwaps should rely on a new "Climate Swaps Provider" (like our many Providers in DaggerfallUnity), which can be overriden by mods
• The default Climate Swaps Provider would work like the current Climate Swaps code, but should also exclude all winter swaps for Rainforest nature sets
• We should probably do the same for WeatherManager, but I'm not sure how moddable it currently is