Backport CE changes for: [Frontend only] Batch comments on merge requests

What does this MR do?

Backports CE changes from https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/7376

What are the relevant issue numbers?

See: https://gitlab.com/gitlab-org/gitlab-ee/issues/1984

(this doesn't close it)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides

app/assets/javascripts/mr_notes/stores/index.js

@@ -6,10 +6,13 @@ import mrPageModule from './modules';
 
 Vue.use(Vuex);
 
-export default new Vuex.Store({
-  modules: {
-    page: mrPageModule,
-    notes: notesModule(),
-    diffs: diffsModule(),
-  },
-});
+export const createStore = () =>
+  new Vuex.Store({
+    modules: {
+      page: mrPageModule,
+      notes: notesModule(),
+      diffs: diffsModule(),
+    },
+  });
+
+export default createStore();