Improve Structures Checking

Improves performance by keying every chunk thats part of a structure to a hashmap
instead of only the first one.

This allows us to avoid iterating the entire structures value set to see
if a block position is inside of a structure.

This should have pretty decent performance improvement to any standard world
that has been around for a whilewith lots of structures due to ineffeciencies
in how MC stores structures (even unloaded chunks has structured data loaded)

scripts/importmcdev.sh

@@ -93,6 +93,9 @@ import PlayerConnectionUtils
 import RegionFile
 import RegistryBlockID
 import RemoteControlListener
+import StructureBoundingBox
+import StructurePiece
+import StructureStart
 import TileEntityEnderChest
 import TileEntityLootable
 import WorldGenStronghold