Image and document choosers don't update content

[cnk]

On Wagtail 4.0.x, the image and document choosers from this package appear to work - popups and navigation are all fine. But when you have chosen the document (or image) and the modal closes, the new content is not incorporated into the text in the editor. There are no errors in the JS console or server logs.

[nickmoreton]

I'll see if this still occurs in #38