Add Actor.HasScene and Script.HasScene

Useful in managed code to check the existence of the scene in hot paths
by avoiding expensive marshalling of the Scene object.

Source/Engine/Scripting/Script.cs

@@ -17,6 +17,12 @@ namespace FlaxEngine
             }
         }
 
+        /// <summary>
+        /// Gets value indicating if the actor owning the script is in a scene.
+        /// </summary>
+        [HideInEditor, NoSerialize]
+        public bool HasScene => Actor?.HasScene ?? false; 
+
         /// <summary>
         /// Gets or sets the world space transformation of the actors owning this script.
         /// </summary>