Merge branch 'ee-38916-add-classlist-polyfill' into 'master'

Add classList polyfill for IE classList.toggle(.., force) -- EE merge edition

Closes gitlab-ce#38916

See merge request gitlab-org/gitlab-ee!3527

app/assets/javascripts/commons/polyfills.js

@@ -10,6 +10,7 @@ import 'core-js/fn/string/from-code-point';
 import 'core-js/fn/symbol';
 
 // Browser polyfills
+import 'classlist-polyfill';
 import './polyfills/custom_event';
 import './polyfills/element';
 import './polyfills/event';

package.json

@@ -24,6 +24,7 @@
     "babel-preset-stage-2": "^6.24.1",
     "bootstrap-sass": "^3.3.6",
     "brace-expansion": "^1.1.8",
+    "classlist-polyfill": "^1.2.0",
     "clipboard": "^1.6.1",
     "compression-webpack-plugin": "^1.0.0",
     "copy-webpack-plugin": "^4.0.1",