Add support for binary modules with native-code only

Source/Tools/Flax.Build/Build/Module.cs

@@ -37,6 +37,11 @@ namespace Flax.Build
         /// </summary>
         public bool BuildNativeCode = true;
 
+        /// <summary>
+        /// True if module has C# code to build. Can be used for native modules without C# bindings nor code.
+        /// </summary>
+        public bool BuildCSharp = true;
+
         /// <summary>
         /// Initializes a new instance of the <see cref="Module"/> class.
         /// </summary>