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/webpacker.yml

@@ -3,8 +3,11 @@
 default: &default
   source_path: app/javascript
   source_entry_path: packs
+  public_root_path: public
   public_output_path: packs
   cache_path: tmp/cache/webpacker
+  check_yarn_integrity: false
+  webpack_compile_output: false
 
   # Additional paths webpack should lookup modules
   # ['app/assets', 'engine/foo/app/assets']
@@ -13,11 +16,31 @@ default: &default
   # Reload manifest.json on all requests so we reload latest compiled packs
   cache_manifest: false
 
+  # Extract and emit a css file
+  extract_css: true
+
+  static_assets_extensions:
+    - .jpg
+    - .jpeg
+    - .png
+    - .tiff
+    - .ico
+    - .svg
+    - .eot
+    - .otf
+    - .ttf
+    - .woff
+    - .woff2
+
   extensions:
+    - .mjs
     - .js
     - .sass
     - .scss
     - .css
+    - .module.sass
+    - .module.scss
+    - .module.css
     - .png
     - .svg
     - .gif
@@ -26,24 +49,38 @@ default: &default
 
 development:
   <<: *default
+
   compile: true
 
+  # Reference: https://webpack.js.org/configuration/dev-server/
   dev_server:
+    https: false
     host: localhost
     port: 3035
+    public: localhost:3035
     hmr: false
-    https: false
+    # Inline should be set to true if using HMR
+    inline: true
+    overlay: true
+    compress: true
+    disable_host_check: true
+    use_local_ip: false
+    quiet: false
+    headers:
+      'Access-Control-Allow-Origin': '*'
+    watch_options:
+      ignored: '**/node_modules/**'
 
 test:
   <<: *default
 
-  # Compile test packs to a separate directory
-  public_output_path: packs-test
-
   # CircleCI precompiles packs prior to running the tests.
   # Also avoids race conditions in parallel_tests.
   compile: false
 
+  # Compile test packs to a separate directory
+  public_output_path: packs-test
+
 production:
   <<: *default