Allow custom biomes to optionally specify color for each leaf type

Allow custom biomes in data packs to specify a color code for each type of leaf block

i.e., optionally allow the "foliage_color" field to be split into "oak_leaves_color, jungle_leaves_color, acacia_leaves_color, dark_oak_leaves_color"

This would allow data pack makers to create custom biomes that have different types of trees with different colors.

For example, an autumn forest biome with trees colored orange, red, and yellow depending on the leaf type.