Embed js height fix (#22141)

* only begin iframe reheight once document state is complete

* format

* lint fixes

* Update public/embed.js to use readystatechange event listener

Co-authored-by: Claire <claire.github-309c@sitedethib.com>

* Call loaded() if ready, otherwise add listenter

* lint fix

Co-authored-by: Claire <claire.github-309c@sitedethib.com>