Fixed inner page tabs not being scrollable

Some inner page tabs where not scrollable like the top nav & this caused
them to break onto new lines mobile.

This pages include:

- dashboard/projects
- project -> merge_requests
- search
- project -> milestones
- project -> pipelines

Closes #18853

app/assets/javascripts/vue_pipelines_index/components/navigation_tabs.js

@@ -17,7 +17,10 @@ export default {
   },
 
   template: `
-    <ul class="nav-links">
+    <div class="scrolling-tabs-container">
+      <div class="fade-left"><i class="fa fa-angle-left"></i></div>
+      <div class="fade-right"><i class="fa fa-angle-right"></i></div>
+      <ul class="nav-links scrolling-tabs">
         <li
           class="js-pipelines-tab-all"
           :class="{ 'active': scope === 'all'}">
@@ -64,5 +67,6 @@ export default {
           <a :href="paths.tagsPath">Tags</a>
         </li>
       </ul>
+    </div>
   `,
 };

app/assets/stylesheets/framework/nav.scss

@@ -476,3 +476,27 @@
     }
   }
 }
+
+.inner-page-scroll-tabs {
+  position: relative;
+
+  .fade-right {
+    @include fade(left, $white-light);
+    right: 0;
+    text-align: right;
+
+    .fa {
+      right: 5px;
+    }
+  }
+
+  .fade-left {
+    @include fade(right, $white-light);
+    left: 0;
+    text-align: left;
+
+    .fa {
+      left: 5px;
+    }
+  }
+}

app/views/dashboard/_projects_head.html.haml

 = content_for :flash_message do
   = render 'shared/project_limit'
-.top-area
-  %ul.nav-links
+.top-area.scrolling-tabs-container
+  .inner-page-scroll-tabs
+    .fade-left= icon('angle-left')
+    .fade-right= icon('angle-right')
+    %ul.nav-links.scrolling-tabs
       = nav_link(page: [dashboard_projects_path, root_path]) do
         = link_to dashboard_projects_path, title: 'Home', class: 'shortcuts-activity', data: {placement: 'right'} do
           Your projects

app/views/projects/merge_requests/_show.html.haml

@@ -52,8 +52,10 @@
       = render 'award_emoji/awards_block', awardable: @merge_request, inline: true
 
     .merge-request-tabs-holder{ class: ("js-tabs-affix" unless ENV['RAILS_ENV'] == 'test') }
-      .merge-request-tabs-container
-        %ul.merge-request-tabs.nav-links.no-top.no-bottom
+      .merge-request-tabs-container.scrolling-tabs-container.inner-page-scroll-tabs
+        .fade-left= icon('angle-left')
+        .fade-right= icon('angle-right')
+        %ul.merge-request-tabs.nav-links.scrolling-tabs
           %li.notes-tab
             = link_to namespace_project_merge_request_path(@project.namespace, @project, @merge_request), data: { target: 'div#notes', action: 'notes', toggle: 'tab' } do
               Discussion

app/views/search/_category.html.haml

-%ul.nav-links.search-filter
+.scrolling-tabs-container.inner-page-scroll-tabs
+  .fade-left= icon('angle-left')
+  .fade-right= icon('angle-right')
+  %ul.nav-links.search-filter.scrolling-tabs
     - if @project
       %li{ class: active_when(@scope == 'blobs') }
         = link_to search_filter_path(scope: 'blobs') do

app/views/shared/milestones/_tabs.html.haml

-%ul.nav-links.no-top.no-bottom
+.scrolling-tabs-container.inner-page-scroll-tabs
+  .fade-left= icon('angle-left')
+  .fade-right= icon('angle-right')
+  %ul.nav-links.scrolling-tabs
     - if milestone.is_a?(GlobalMilestone) || can?(current_user, :read_issue, @project)
       %li.active
         = link_to '#tab-issues', 'data-toggle' => 'tab', 'data-show' => '.tab-issues-buttons' do

changelogs/unreleased/scrollable-secondary-tabs.yml

+---
+title: Fixed tabs not scrolling on mobile
+merge_request:
+author: