Fixed changing item bugs with Menu, added Menu#allowsChangingHeldItem

eco-api/src/main/java/com/willfp/eco/core/gui/menu/Menu.java

@@ -162,6 +162,15 @@ public interface Menu {
      */
     void refresh(@NotNull Player player);
 
+    /**
+     * If the menu allows changing the held item.
+     *
+     * @return If allowed.
+     */
+    default boolean allowsChangingHeldItem() {
+        return false;
+    }
+
     /**
      * Call a menu event.
      *

eco-api/src/main/java/com/willfp/eco/core/gui/menu/MenuBuilder.java

@@ -186,6 +186,15 @@ public interface MenuBuilder extends PageBuilder {
         return this;
     }
 
+    /**
+     * Allow the player to change their held item.
+     *
+     * @return The builder.
+     */
+    default MenuBuilder allowChangingHeldItem() {
+        return this;
+    }
+
     /**
      * Build the menu.
      *