[camera] Refactor Radio widgets in example

Refactors the camera example to use a new `RadioGroup` widget. This removes deprecated `groupValue` and `onChanged` properties from each individual `RadioListTile` and moves them to the parent `RadioGroup`.

Author: alexskobozev

packages/camera/camera_android/example/lib/main.dart

@@ -599,16 +599,18 @@ class _CameraExampleHomeState extends State<CameraExampleHome>
             width: 90.0,
             child: RadioListTile<CameraDescription>(
               title: Icon(getCameraLensIcon(cameraDescription.lensDirection)),
-              groupValue: controller?.description,
               value: cameraDescription,
-              onChanged: onChanged,
             ),
           ),
         );
       }
     }
 
-    return Row(children: toggles);
+    return RadioGroup<CameraDescription>(
+      groupValue: controller?.description,
+      onChanged: onChanged,
+      child: Row(children: toggles),
+    );
   }
 
   String timestamp() => DateTime.now().millisecondsSinceEpoch.toString();