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>

app/views/layouts/admin.html.haml

@@ -6,7 +6,7 @@
     .sidebar-wrapper
       .sidebar
         = link_to root_path do
-          = image_tag asset_pack_path('logo.svg'), class: 'logo', alt: 'Mastodon'
+          = image_pack_tag 'logo.svg', class: 'logo', alt: 'Mastodon'
 
         = render_navigation
     .content-wrapper

app/views/layouts/auth.html.haml

@@ -6,7 +6,7 @@
     .logo-container
       %h1
         = link_to root_path do
-          = image_tag asset_pack_path('logo_full.svg'), alt: 'Mastodon'
+          = image_pack_tag 'logo_full.svg', alt: 'Mastodon'
 
     .form-container
       = render 'flashes'

app/views/layouts/mailer.html.haml

@@ -24,7 +24,7 @@
                               %tr
                                 %td.column-cell
                                   = link_to root_url do
-                                    = image_tag full_pack_url('logo_full.png'), alt: 'Mastodon', height: 34, class: 'logo'
+                                    = image_tag full_pack_url('media/images/mailer/logo_full.png'), alt: 'Mastodon', height: 34, class: 'logo'
 
     = yield
 
@@ -49,4 +49,4 @@
                                 %p= link_to t('application_mailer.notification_preferences'), settings_notifications_url
                               %td.column-cell.text-right
                                 = link_to root_url do
-                                  = image_tag full_pack_url('logo_transparent.png'), alt: 'Mastodon', height: 24
+                                  = image_tag full_pack_url('media/images/mailer/logo_transparent.png'), alt: 'Mastodon', height: 24

app/views/layouts/public.html.haml

@@ -8,7 +8,7 @@
         %nav.header
           .nav-left
             = link_to root_url, class: 'brand' do
-              = image_tag asset_pack_path('logo_full.svg'), alt: 'Mastodon'
+              = image_pack_tag 'logo_full.svg', alt: 'Mastodon'
 
             = link_to t('directories.directory'), explore_path, class: 'nav-link optional' if Setting.profile_directory
             = link_to t('about.about_this'), about_more_path, class: 'nav-link optional'