Provide isRouteErrorResponse in react-server environments (#14166)

Author: markdalgleish

.changeset/gorgeous-dragons-hang.md

@@ -0,0 +1,5 @@
+---
+"react-router": patch
+---
+
+Provide `isRouteErrorResponse` utility in `react-server` environments

packages/react-router/index-react-server.ts

@@ -47,6 +47,7 @@ export { createStaticHandler } from "./lib/router/router";
 export {
   data,
   matchRoutes,
+  isRouteErrorResponse,
   unstable_createContext,
   unstable_RouterContextProvider,
 } from "./lib/router/utils";