make sure split-view diff discussions are made visible by "toggle comments" button

CHANGELOG

@@ -13,6 +13,7 @@ v 8.13.0 (unreleased)
   - Revoke button in Applications Settings underlines on hover.
   - Update ruby-prof to 0.16.2. !6026 (Elan Ruusamäe)
   - Add organization field to user profile
+  - Fix resolved discussion display in side-by-side diff view !6575
   - Optimize GitHub importing for speed and memory
   - API: expose pipeline data in builds API (!6502, Guilherme Salazar)
 

app/assets/javascripts/application.js

@@ -247,7 +247,7 @@
       $this.toggleClass('active');
       var notesHolders = $this.closest('.diff-file').find('.notes_holder');
       if ($this.hasClass('active')) {
-        notesHolders.show();
+        notesHolders.show().find('.hide').show();
       } else {
         notesHolders.hide();
       }