Add a generic "Cave" biome for world generation

Adding a "Cave" biome for caves that aren't Lush, Dripstone or Deep Dark would solve two current problems we have underground.

1. Grass, foliage and water color. Underground as low as bedrock, you can still see aquifers of murky swamp water or dead leaves under a desert. A "cave" biome would solve these by having its own grass, foliage and water colors.

2. Bedrock Edition worldspawn mechanics. Inside the Bedrock Edition of the game, you can only spawn on a few select biomes. However, you can still spawn inside a cave since they technically count as the biomes above them. The "cave" biome would fix this by not being part of the list of valid spawn biomes.