Specify ErrorResponse as interface to provide obvious contract

.changeset/error-response-type.md

@@ -0,0 +1,5 @@
+---
+"@remix-run/router": patch
+---
+
+Fix `ErrorResponse` type to avoid leaking internal field

contributors.yml

@@ -238,3 +238,4 @@
 - yionr
 - yuleicul
 - zheng-chuang
+- sgrishchenko

packages/router/utils.ts

@@ -1533,11 +1533,21 @@ export const redirectDocument: RedirectFunction = (url, init) => {
   return response;
 };
 
+export type ErrorResponse = {
+  status: number;
+  statusText: string;
+  data: any;
+};
+
 /**
  * @private
  * Utility class we use to hold auto-unwrapped 4xx/5xx Response bodies
+ *
+ * We don't export the class for public use since it's an implementation
+ * detail, but we export the interface above so folks can build their own
+ * abstractions around instances via isRouteErrorResponse()
  */
-export class ErrorResponseImpl {
+export class ErrorResponseImpl implements ErrorResponse {
   status: number;
   statusText: string;
   data: any;
@@ -1562,11 +1572,6 @@ export class ErrorResponseImpl {
   }
 }
 
-// We don't want the class exported since usage of it at runtime is an
-// implementation detail, but we do want to export the shape so folks can
-// build their own abstractions around instances via isRouteErrorResponse()
-export type ErrorResponse = InstanceType<typeof ErrorResponseImpl>;
-
 /**
  * Check if the given error is an ErrorResponse generated from a 4xx/5xx
  * Response thrown from an action/loader