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)

Spigot-Server-Patches/Fix-MC-117075-TE-Unload-Lag-Spike.patch

@@ -4,18 +4,6 @@ Date: Wed, 9 Aug 2017 17:51:22 -0500
 Subject: [PATCH] Fix MC-117075: TE Unload Lag Spike
 
 
-diff --git a/src/main/java/net/minecraft/server/ChunkCoordIntPair.java b/src/main/java/net/minecraft/server/ChunkCoordIntPair.java
-index 239440888..e8d1a1c60 100644
---- a/src/main/java/net/minecraft/server/ChunkCoordIntPair.java
-+++ b/src/main/java/net/minecraft/server/ChunkCoordIntPair.java
-@@ -0,0 +0,0 @@ public class ChunkCoordIntPair {
-         this.z = blockposition.getZ() >> 4;
-     }
- 
-+    public static long asLong(int x, int z) { return a(x, z); } // Paper - OBFHELPER
-     public static long a(int i, int j) {
-         return (long) i & 4294967295L | ((long) j & 4294967295L) << 32;
-     }
 diff --git a/src/main/java/net/minecraft/server/World.java b/src/main/java/net/minecraft/server/World.java
 index 30cf4a251..f690aaa10 100644
 --- a/src/main/java/net/minecraft/server/World.java