Maintain scroll position on iframe reload

[samason]

When the iframe pane is being used as a live preview, it would be ideal if on revision of a given content type that the iframe maintained its scroll position when reloaded.

[samason]

Update on this in case anyone else is interested in the future:

I made an adjustment to the plugin to have this work locally that avoids any CORS issues. What I'm doing is instead of updating the src attribute of the iframe on reload, I'm using the fetch API on my source URL on reload, grabbing the HTML, and putting that into the srcdoc attribute. By updating the inner HTML of the iframe, you do not have to adjust your scroll position, and in order to do that without cross-origin issues, the HTML within the iframe must be inline.

I'm not making a PR for this since it's kind of hack-y and probably goes against most peoples use case but if there's interest I can share more details.