Add page helper methods for notesApp

app/assets/javascripts/lib/utils/dom_utils.js

-/* eslint-disable import/prefer-default-export */
+import $ from 'jquery';
+import { isInIssuePage, isInMRPage, isInEpicPage, hasVueMRDiscussionsCookie } from './common_utils';
+
+const isVueMRDiscussions = () => isInMRPage() && hasVueMRDiscussionsCookie() && !$('#diffs').is(':visible');
 
 export const addClassIfElementExists = (element, className) => {
   if (element) {
     element.classList.add(className);
   }
 };
+
+export const isInVueNoteablePage = () => isInIssuePage() || isInEpicPage() || isVueMRDiscussions();