Update world map check to new API

Assets/Scripts/ARWorldMapController.cs

         get
         {
 #if UNITY_IOS
-            var sessionSubsystem = (ARKitSessionSubsystem)m_ARSession.subsystem;
-            if (sessionSubsystem != null)
-                return sessionSubsystem.worldMapSupported;
+            return m_ARSession.subsystem is ARKitSessionSubsystem && ARKitSessionSubsystem.worldMapSupported;
+#else
+            return false;
-            return false;
         }
     }