Fix TypeError when Bootstrap is included in head (#32024)

* extend jquery after domContentLoaded event is fired

* add unittest for util onDOMContentLoaded

* wait for trigger jquery event after domContentLoaded

* remove domcontentready from eventHandler

* move istanbul ignore statements to correct line

Co-authored-by: XhmikosR <xhmikosr@gmail.com>

js/src/util/index.js

@@ -180,8 +180,15 @@ const getjQuery = () => {
   return null
 }
 
+const onDOMContentLoaded = callback => {
+  if (document.readyState === 'loading') {
+    document.addEventListener('DOMContentLoaded', callback)
+  } else {
+    callback()
+  }
+}
+
 export {
-  getjQuery,
   TRANSITION_END,
   getUID,
   getSelectorFromElement,
@@ -194,5 +201,7 @@ export {
   isVisible,
   findShadowRoot,
   noop,
-  reflow
+  reflow,
+  getjQuery,
+  onDOMContentLoaded
 }