fix(Visual): add UnityFlag attribute to meshesToModify field

The meshesToModify field needs to have the UnityFlag attribute on it
otherwise it won't show up the multiple choice enum drop down.

Runtime/Visual/MeshStateModifier.cs

@@ -4,6 +4,7 @@ namespace Zinnia.Visual
     using System.Collections.Generic;
     using UnityEngine;
     using UnityEngine.Events;
+    using Zinnia.Data.Attribute;
     using Zinnia.Data.Collection.List;
     using Zinnia.Extension;
 
@@ -38,6 +39,7 @@ public enum MeshTypes
         [Header("Mesh Settings")]
         [Tooltip("The mesh components to modify.")]
         [SerializeField]
+        [UnityFlags]
         private MeshTypes meshesToModifiy = (MeshTypes)(-1);
         /// <summary>
         /// The mesh components to modify.