Bump webpacker from 3.5.5 to 4.0.2 (#10277)

Bumps [webpacker](https://github.com/rails/webpacker) from 3.5.5 to 4.0.2.
- [Release notes](https://github.com/rails/webpacker/releases)
- [Changelog](https://github.com/rails/webpacker/blob/master/CHANGELOG.md)
- [Commits](https://github.com/rails/webpacker/compare/v3.5.5...v4.0.2)

Signed-off-by: dependabot[bot] <support@dependabot.com>
Co-authored-by: Yamagishi Kazutoshi <ykzts@desire.sh>

config/webpack/rules/babel.js

@@ -0,0 +1,21 @@
+const { join, resolve } = require('path');
+const { env, settings } = require('../configuration');
+
+module.exports = {
+  test: /\.(js|jsx|mjs)$/,
+  include: [
+    settings.source_path,
+    ...settings.resolved_paths,
+  ].map(p => resolve(p)),
+  exclude: /node_modules/,
+  use: [
+    {
+      loader: 'babel-loader',
+      options: {
+        cacheDirectory: join(settings.cache_path, 'babel-loader'),
+        cacheCompression: env.NODE_ENV === 'production',
+        compact: env.NODE_ENV === 'production',
+      },
+    },
+  ],
+};