Add NoUndo attribute for properties without undo usage

Source/Engine/Scripting/Attributes/Editor/NoUndoAttribute.cs

@@ -0,0 +1,15 @@
+// Copyright (c) 2012-2021 Wojciech Figat. All rights reserved.
+
+using System;
+
+namespace FlaxEngine
+{
+    /// <summary>
+    /// Makes a property to not use undo/redo when modifying it in Editor.
+    /// </summary>
+    [Serializable]
+    [AttributeUsage(AttributeTargets.Field | AttributeTargets.Property)]
+    public sealed class NoUndoAttribute : Attribute
+    {
+    }
+}