Merge branch 'fix-diff-comments-bug' into 'master'

Fix diff comments inverted toggle bug

## What does this MR do?
Explicitly set the comments visibility toggle based on the `active` css class.

## Are there points in the code the reviewer needs to double check?
Shouldn't be

## Why was this MR needed?
Fixes existing UI bug

## What are the relevant issue numbers?
Closes #20898 

## Screenshots (if relevant)
Before:
![A1ccIDEWsI](/uploads/21175e2008ee4e00225c22afebd873aa/A1ccIDEWsI.gif)

After:
![jHoFp69mAK](/uploads/e85f429d60a4e56d588faec51cd8648a/jHoFp69mAK.gif)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5818

CHANGELOG

@@ -88,6 +88,7 @@ v 8.11.0 (unreleased)
   - Allow branch names ending with .json for graph and network page !5579 (winniehell)
   - Add the `sprockets-es6` gem
   - Improve OAuth2 client documentation (muteor)
+  - Fix diff comments inverted toggle bug (ClemMakesApps)
   - Multiple trigger variables show in separate lines (Katarzyna Kobierska Ula Budziszewska)
   - Profile requests when a header is passed
   - Avoid calculation of line_code and position for _line partial when showing diff notes on discussion tab.

app/assets/javascripts/application.js

@@ -223,8 +223,11 @@
       return $('.navbar-toggle').toggleClass('active');
     });
     $body.on("click", ".js-toggle-diff-comments", function(e) {
-      $(this).toggleClass('active');
-      $(this).closest(".diff-file").find(".notes_holder").toggle();
+      var $this = $(this);
+      var showComments = $this.hasClass('active');
+
+      $this.toggleClass('active');
+      $this.closest(".diff-file").find(".notes_holder").toggle(showComments);
       return e.preventDefault();
     });
     $document.off("click", '.js-confirm-danger');