feat(route-tables): add function to check route to CloudWAN Network

- Implemented  to determine if a subnet has a route to a CloudWAN Network.
- The function checks the associated route table for routes with  and a destination CIDR of .

packages/aws-cdk/lib/context-providers/vpcs.ts

@@ -234,6 +234,17 @@ class RouteTables {
     );
   }
 
+  /**
+   * Whether the given subnet has a route to a CloudWAN Network
+   */
+  public hasRouteToCloudWAN(subnetId: string | undefined): boolean {
+    const table = this.tableForSubnet(subnetId) || this.mainRouteTable;
+
+    return (
+      !!table && !!table.Routes && table.Routes.some((route) => !!route.CoreNetworkArn && route.DestinationCidrBlock === '0.0.0.0/0')
+    );
+  }
+
   public tableForSubnet(subnetId: string | undefined) {
     return this.tables.find(
       (table) => !!table.Associations && table.Associations.some((assoc) => assoc.SubnetId === subnetId),