Decreased watchpack aggregate timeout (#54461)

This decreases the aggregate event timeout for WatchPack in development to `5ms` which should improve the performance of reloading routes for users developing Next.js applications.

packages/next/src/server/lib/router-utils/setup-dev.ts

@@ -87,6 +87,13 @@ import { MiddlewareManifest } from '../../../build/webpack/plugins/middleware-pl
 import { devPageFiles } from '../../../build/webpack/plugins/next-types-plugin/shared'
 import type { RenderWorkers } from '../router-server'
 
+/**
+ * This is the timeout for which the watchpack will emit the `aggregate` event
+ * after file changes are made. This is to prevent unnecessary rebuilds when
+ * multiple files are changed at once.
+ */
+const WATCHPACK_AGGREGATE_TIMEOUT = 5
+
 type SetupOpts = {
   renderWorkers: RenderWorkers
   dir: string
@@ -780,6 +787,7 @@ async function startWatcher(opts: SetupOpts) {
     files.push(...tsconfigPaths)
 
     const wp = new Watchpack({
+      aggregateTimeout: WATCHPACK_AGGREGATE_TIMEOUT,
       ignored: (pathname: string) => {
         return (
           !files.some((file) => file.startsWith(pathname)) &&