Improvements to BlockStates

* Update Javadoc of block state classes to better match implementation behaviour.
* Add Container interface which provides access to the snapshot inventory.

By: Lukas Hennig <lukas@wirsindwir.de>

paper-api/src/main/java/org/bukkit/block/Furnace.java

@@ -2,12 +2,11 @@ package org.bukkit.block;
 
 import org.bukkit.Nameable;
 import org.bukkit.inventory.FurnaceInventory;
-import org.bukkit.inventory.InventoryHolder;
 
 /**
- * Represents a furnace.
+ * Represents a captured state of a furnace.
  */
-public interface Furnace extends BlockState, InventoryHolder, Lockable, Nameable {
+public interface Furnace extends Container, Nameable {
 
     /**
      * Get burn time.
@@ -37,5 +36,9 @@ public interface Furnace extends BlockState, InventoryHolder, Lockable, Nameable
      */
     public void setCookTime(short cookTime);
 
+    @Override
     public FurnaceInventory getInventory();
+
+    @Override
+    public FurnaceInventory getSnapshotInventory();
 }