Update JS to update fa-chevron-up to GitLab SVG

Using a similar pattern to the JS functionality in
app/assets/javascripts/right_sidebar.js.

app/assets/javascripts/behaviors/toggler_behavior.js

@@ -12,11 +12,19 @@ import { getLocationHash } from '../lib/utils/url_utility';
 $(() => {
   function toggleContainer(container, toggleState) {
     const $container = $(container);
-
-    $container
-      .find('.js-toggle-button .fa-chevron-up, .js-toggle-button .fa-chevron-down')
-      .toggleClass('fa-chevron-up', toggleState)
-      .toggleClass('fa-chevron-down', toggleState !== undefined ? !toggleState : undefined);
+    const isExpanded = $container.data('is-expanded');
+    const $collapseIcon = $container.find('.js-sidebar-collapse');
+    const $expandIcon = $container.find('.js-sidebar-expand');
+
+    if (isExpanded) {
+      $container.data('is-expanded', false);
+      $collapseIcon.addClass('hidden');
+      $expandIcon.removeClass('hidden');
+    } else {
+      $container.data('is-expanded', true);
+      $expandIcon.addClass('hidden');
+      $collapseIcon.removeClass('hidden');
+    }
 
     $container.find('.js-toggle-content').toggle(toggleState);
   }

app/views/discussions/_discussion.html.haml

@@ -2,17 +2,15 @@
 %li.note.note-discussion.timeline-entry.unstyled-comments
   .timeline-entry-inner
     .timeline-content
-      .discussion.js-toggle-container{ data: { discussion_id: discussion.id } }
+      .discussion.js-toggle-container{ data: { discussion_id: discussion.id, is_expanded: expanded.to_s } }
         .discussion-header
           .timeline-icon
             = link_to user_path(discussion.author) do
               = image_tag avatar_icon_for_user(discussion.author), class: "avatar s40"
           .discussion-actions
             %button.note-action-button.discussion-toggle-button.js-toggle-button{ type: "button", class: ("js-toggle-lazy-diff" unless expanded) }
-              - if expanded
-                = icon("chevron-up")
-              - else
-                = icon("chevron-down")
+              = sprite_icon('chevron-up', css_class: "js-sidebar-collapse #{'hidden' unless expanded}")
+              = sprite_icon('chevron-down', css_class: "js-sidebar-expand #{'hidden' if expanded}")
               = _('Toggle thread')
           = link_to_member(@project, discussion.author, avatar: false)