SPIGOT-1039: Improve DoubleChest semantics

By: md_5 <git@md-5.net>

paper-server/src/main/java/org/bukkit/craftbukkit/inventory/CraftInventoryDoubleChest.java

@@ -8,6 +8,7 @@ import org.bukkit.inventory.Inventory;
 import org.bukkit.inventory.ItemStack;
 
 import net.minecraft.server.InventoryLargeChest;
+import org.bukkit.Location;
 
 public class CraftInventoryDoubleChest extends CraftInventory implements DoubleChestInventory {
     private final CraftInventory left;
@@ -59,4 +60,9 @@ public class CraftInventoryDoubleChest extends CraftInventory implements DoubleC
     public DoubleChest getHolder() {
         return new DoubleChest(this);
     }
+
+    @Override
+    public Location getLocation() {
+        return getLeftSide().getLocation().add(getRightSide().getLocation()).multiply(0.5);
+    }
 }