improvement: use mutation observer to replace mutation events when available

[YongYuH]

Description

• Mutation events is a deprecated feature in mutation event MDN docs. Use Mutation Observer as a replacement api if the browser supports.

• Fix warning in browser

  [Violation] Added synchronous DOM mutation listener to a 'DOMNodeInserted' event. Consider using MutationObserver to make the page more responsive.

Type of change

• [x] Improvement (backwards-compatible enhancement)