Update webpack documentation (#3777)

Co-authored-by: Sasha Koss <koss@nocorp.me>

docs/webpack.md

@@ -16,11 +16,11 @@ export const supportedLocales = ["en-US", "de", "pl", "it"];
 We could also have a function that formats the date:
 
 ```js
-const getLocale = (locale) => import(`date-fns/locale/${locale}/index.js`); // or require() if using CommonJS
+const getLocale = (locale) => import(`date-fns-locale/locale/${locale}.mjs`); // or require() if using CommonJS
 
 const formatDate = (date, formatStyle, locale) => {
   return format(date, formatStyle, {
-    locale: getLocale(locale),
+    locale: getLocale(locale).default,
   });
 };
 ```
@@ -30,17 +30,22 @@ In order to exclude unused languages we can use webpacks [ContextReplacementPlug
 `webpack.config.js`:
 
 ```js
-import webpack from 'webpack'
-import { supportedLocales } from './config.js'
-
-export default const config = {
+import webpack from "webpack";
+import { supportedLocales } from "./config.js";
+
+export default config = {
+  resolve: {
+    alias: {
+      "date-fns-locale": path.dirname(require.resolve("date-fns/package.json")),
+    },
+  },
   plugins: [
     new webpack.ContextReplacementPlugin(
-      /^date-fns[/\\]locale$/,
-      new RegExp(`\\.[/\\\\](${supportedLocales.join('|')})[/\\\\]index\\.js$`)
-    )
-  ]
-}
+      /date-fns[/\\]locale/,
+      new RegExp(`(${locales.join("|")})\.mjs$`),
+    ),
+  ],
+};
 ```
 
 This results in a language bundle of ~23kb .