added shader source and removed unused variables/includes

Source/Editor/Content/Proxy/ShaderSourceProxy.cs

@@ -13,6 +13,7 @@ namespace FlaxEditor.Content
     /// Context proxy object for shader source files (represented by <see cref="ShaderSourceItem"/>).
     /// </summary>
     /// <seealso cref="FlaxEditor.Content.ContentProxy" />
+    [ContentContextMenu("New/Shader Source")]
     public class ShaderSourceProxy : ContentProxy
     {
         /// <inheritdoc />

Source/Editor/Windows/ContentWindow.ContextMenu.cs

@@ -1,14 +1,10 @@
 // Copyright (c) 2012-2022 Wojciech Figat. All rights reserved.
 
 using System;
-using System.CodeDom;
-using System.Collections.Generic;
-using System.Linq;
 using FlaxEditor.Content;
 using FlaxEditor.GUI.ContextMenu;
 using FlaxEngine;
 using FlaxEngine.Assertions;
-using FlaxEngine.GUI;
 using FlaxEngine.Json;
 
 namespace FlaxEditor.Windows
@@ -43,7 +39,6 @@ namespace FlaxEditor.Windows
 
             // Create context menu
             ContextMenuButton b;
-            ContextMenuChildMenu c;
             ContextMenu cm = new ContextMenu
             {
                 Tag = item