Override hashCode method in AbstractRegion

This commit fixes the PlotSquared issue where running a PlotSquared command could result in intense lag on the main thread. This was mainly seen with running the /p info command on an extremely large plot.

Since #world can be null, the uniqueness of this hashCode is not the best, but since it's essentially just a collection of BlockVector3's, I don't believe this change will break anything. If it does, please let me know! Feedback on the uniqueness of this is welcomed.

worldedit-core/src/main/java/com/sk89q/worldedit/regions/AbstractRegion.java

@@ -212,4 +212,12 @@ public abstract class AbstractRegion extends AbstractSet<BlockVector3> implement
         return chunks;
     }
 
+    @Override
+    public int hashCode() {
+        int worldHash = this.world == null ? 7 : this.world.hashCode();
+        int result = worldHash ^ (worldHash >>> 32);
+        result = 31 * result + this.getMinimumPoint().hashCode();
+        result = 31 * result + this.getMaximumPoint().hashCode();
+        return result;
+    }
 }