Merge branch 'remove-unique-keyframes' into 'master'

Replace unique keyframes mixin with specific keyframe animation names

## What does this MR do?
Replaces `unique-keyframes` mixin with `include-keyframes` mixin

## Are there points in the code the reviewer needs to double check?
Shouldn't be :thumbsup_tone1: 

## Why was this MR needed?
Some users had GitLab hosted in a distributed environment that makes `unique-keyframes` a non-viable implementation. 
The randomized animation names from `unique-keyframes` was not being picked up by the different servers which resulted in 404 errors.

## Screenshots (if relevant)
None

## 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 [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [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)

## What are the relevant issue numbers?
Closes #22629

See merge request !6603

1 files changed, 7 insertions, 0 deletions

diff --git a/app/assets/stylesheets/framework/mixins.scss b/app/assets/stylesheets/framework/mixins.scss
index 7c207969b0a..7fabf27a558 100644
--- a/app/assets/stylesheets/framework/mixins.scss
+++ b/app/assets/stylesheets/framework/mixins.scss
@@ -84,3 +84,10 @@
     @content;
   }
 }
+
+@mixin include-keyframes($animation-name) {
+  @include webkit-prefix(animation-name, $animation-name);
+  @include keyframes($animation-name) {
+    @content;
+  }
+}