Add gravel layer, one layer add ambient to all forest and shores

Adding layers to the gravel, that only can be farmed by the shovel, dont fill inventory and add a functionality a lot of people want, some rocks into several forest, and maybe in the rocky shores where gravel is spawn normally. Doing only in dry biomes, because underwater they flow until made full blocks.

Same in sand maybe, but i dont see any function more than make sandstorms in desert biome