Grimcraft 4.0

Heavily Optimized the datapack, added the final content.
Fixed Bugs, Buffed the Royal Skeleton, fixed the Leviathan's AI, Royal Skeleton's structure can only spawn in plains, optimized the datapack.
The Nether War Hog can actually be summoned again.
Added the Piglin War Horn, added advancements to fit with the Unified Installed Data Pack View, function grimcraft:uninstall works properly.