[1.5.4] Fix accessibility level

Runtime/cupertino/route.cs

                 return false;
             }
 
-            if (route._hasScopedWillPopCallback) {
+            if (route.hasScopedWillPopCallback) {
                 return false;
             }
 

Runtime/widgets/pages.cs

         public override bool canTransitionFrom(TransitionRoute previousRoute) {
             return previousRoute is PageRoute;
         }
-        
-        public bool _hasScopedWillPopCallback => this.hasScopedWillPopCallback;
 
         public override AnimationController createAnimationController() {
             var controller = base.createAnimationController();

Runtime/widgets/routes.cs

             this._willPopCallbacks.Remove(callback);
         }
 
-        protected bool hasScopedWillPopCallback {
+        protected internal bool hasScopedWillPopCallback {
             get { return this._willPopCallbacks.isNotEmpty(); }
         }