Because the courseware microfrontend loads units inside iframes,
the LTI modal ends up being squished and generally ugly.
This PR introduces a new message sent to the parent window to request
a modal containing the contents of the LTI launch iframe.

https://openedx.atlassian.net/browse/TNL-7410

Toggle aria-hidden attribute on modal window open/close; Set title attribute on iframe to display name of component; Remove aria-labelledby attribute from modal body; Make modal overlay id attribute unique'