Move jest jquery setup and add commons import

- This loads all of our default jquery plugins
- This also removes the need for our custom mocker to
  handle node_modules things
- Originally I wanted to import just ~/commons but this
  seems to load some modules which depend on API and broke
  the mocking in those tests
  (user_merge_requests_spec)

spec/frontend/helpers/jquery.js

 import $ from 'jquery';
 
+// Expose jQuery so specs using jQuery plugins can be imported nicely.
+// Here is an issue to explore better alternatives:
+// https://gitlab.com/gitlab-org/gitlab/issues/12448
 global.$ = $;
 global.jQuery = $;
 
+// Fail tests for unmocked requests
+$.ajax = () => {
+  const err = new Error(
+    'Unexpected unmocked jQuery.ajax() call! Make sure to mock jQuery.ajax() in tests.',
+  );
+  global.fail(err);
+  throw err;
+};
+
 export default $;

spec/frontend/mocks/node/jquery.js

-/* eslint-disable import/no-commonjs */
-
-const $ = jest.requireActual('jquery');
-
-// Fail tests for unmocked requests
-$.ajax = () => {
-  const err = new Error(
-    'Unexpected unmocked jQuery.ajax() call! Make sure to mock jQuery.ajax() in tests.',
-  );
-  global.fail(err);
-  throw err;
-};
-
-// jquery is not an ES6 module
-module.exports = $;

spec/frontend/test_setup.js

 import Vue from 'vue';
 import * as jqueryMatchers from 'custom-jquery-matchers';
-import $ from 'jquery';
 import { config as testUtilsConfig } from '@vue/test-utils';
 import Translate from '~/vue_shared/translate';
 import { initializeTestTimeout } from './helpers/timeout';
@@ -9,11 +8,9 @@ import { setupManualMocks } from './mocks/mocks_helper';
 import customMatchers from './matchers';
 
 import './helpers/dom_shims';
-
-// Expose jQuery so specs using jQuery plugins can be imported nicely.
-// Here is an issue to explore better alternatives:
-// https://gitlab.com/gitlab-org/gitlab/issues/12448
-window.jQuery = $;
+import './helpers/jquery';
+import '~/commons/jquery';
+import '~/commons/bootstrap';
 
 process.on('unhandledRejection', global.promiseRejectionHandler);