Merge branch 'ee-12257-sidebar-mediator' into 'master'

EE port of: Removes EE differences for app/assets/javascripts/sidebar/sidebar_mediator.js

See merge request gitlab-org/gitlab-ee!14392

app/assets/javascripts/sidebar/sidebar_mediator.js

-import Store from 'ee/sidebar/stores/sidebar_store';
 import { visitUrl } from '../lib/utils/url_utility';
 import Flash from '../flash';
 import Service from './services/sidebar_service';
+import Store from 'ee_else_ce/sidebar/stores/sidebar_store';
 import { __ } from '~/locale';
 
 export default class SidebarMediator {