Unsaved changes popup

<img width="282" alt="image" src="https://user-images.githubusercontent.com/1150196/155597094-4a1f724f-a190-41b7-947c-d4989a68cb9c.png">

When a form is using the select interface and you try to leave or refresh the page, the unsaved fields notice appears.
Also see: https://wordpress.org/support/topic/your-changes-were-not-saved/