MutationCallback Delegate
https://dom.spec.whatwg.org/#callbackdef-mutationcallback
public delegate void MutationCallback(IReadOnlyList<MutationRecord> mutations, MutationObserver observer)https://dom.spec.whatwg.org/#callbackdef-mutationcallback
public delegate void MutationCallback(IReadOnlyList<MutationRecord> mutations, MutationObserver observer)