fix(@angular/ssr): allow using function with optional request context argument

Author: pieh

packages/angular/ssr/src/handler.ts

@@ -10,12 +10,14 @@
  * Function for handling HTTP requests in a web environment.
  *
  * @param request - The incoming HTTP request object.
+ * @param requestContext - Optional context for rendering, such as metadata associated with the request.
  * @returns A Promise resolving to a `Response` object, `null`, or directly a `Response`,
  * supporting both synchronous and asynchronous handling.
  * @developerPreview
  */
 export type RequestHandlerFunction = (
   request: Request,
+  requestContext?: unknown,
 ) => Promise<Response | null> | null | Response;
 
 /**