Fix pikaday being undefined

Closes #36207

app/assets/javascripts/due_date_select.js

 /* eslint-disable wrap-iife, func-names, space-before-function-paren, comma-dangle, prefer-template, consistent-return, class-methods-use-this, arrow-body-style, no-unused-vars, no-underscore-dangle, no-new, max-len, no-sequences, no-unused-expressions, no-param-reassign */
 /* global dateFormat */
-/* global Pikaday */
 
+import Pikaday from 'pikaday';
 import DateFix from './lib/utils/datefix';
 
 class DueDateSelect {

app/assets/javascripts/issuable_form.js

@@ -2,8 +2,8 @@
 /* global GitLab */
 /* global Autosave */
 /* global dateFormat */
-/* global Pikaday */
 
+import Pikaday from 'pikaday';
 import UsersSelect from './users_select';
 import GfmAutoComplete from './gfm_auto_complete';
 import ZenMode from './zen_mode';

app/assets/javascripts/main.js

@@ -7,7 +7,6 @@
 import jQuery from 'jquery';
 import _ from 'underscore';
 import Cookies from 'js-cookie';
-import Pikaday from 'pikaday';
 import Dropzone from 'dropzone';
 import Sortable from 'vendor/Sortable';
 
@@ -20,7 +19,6 @@ import 'vendor/fuzzaldrin-plus';
 window.jQuery = jQuery;
 window.$ = jQuery;
 window._ = _;
-window.Pikaday = Pikaday;
 window.Dropzone = Dropzone;
 window.Sortable = Sortable;
 

app/assets/javascripts/member_expiration_date.js

-/* global Pikaday */
 /* global dateFormat */
+
+import Pikaday from 'pikaday';
+
 (() => {
   // Add datepickers to all `js-access-expiration-date` elements. If those elements are
   // children of an element with the `clearable-input` class, and have a sibling