Add ModuleInitializer attribute for C# scripting initialization code running on load

Source/Engine/Scripting/Attributes/ModuleInitializerAttribute.cs

@@ -0,0 +1,14 @@
+// Copyright (c) 2012-2022 Wojciech Figat. All rights reserved.
+
+using System;
+
+namespace FlaxEngine
+{
+    /// <summary>
+    /// Indicates that a static class initializes the code module. All static, void and parameterless methods within the class will be invoked upon module loading.
+    /// </summary>
+    [AttributeUsage(AttributeTargets.Class)]
+    public sealed class ModuleInitializerAttribute : Attribute
+    {
+    }
+}