SPIGOT-7554, #954: Add DecoratedPotInventory

By: BlackHole <black-hole@live.com>

paper-api/src/main/java/org/bukkit/inventory/DecoratedPotInventory.java

@@ -0,0 +1,29 @@
+package org.bukkit.inventory;
+
+import org.bukkit.block.DecoratedPot;
+import org.jetbrains.annotations.Nullable;
+
+/**
+ * Interface to the inventory of a DecoratedPot.
+ */
+public interface DecoratedPotInventory extends Inventory {
+
+    /**
+     * Set the item stack in the decorated pot.
+     *
+     * @param item the new item stack
+     */
+    public void setItem(@Nullable ItemStack item);
+
+    /**
+     * Get the item stack in the decorated pot.
+     *
+     * @return the current item stack
+     */
+    @Nullable
+    public ItemStack getItem();
+
+    @Nullable
+    @Override
+    public DecoratedPot getHolder();
+}