Improve layout/block field errors

Currently when you have a required field inside a block you “only” get the popup telling you that there is an error. The text is specific but it can get tricky, especially when combined with the layout field, to track down the block that actually has the error.

Imageine you have more than 10 layout rows on your page and you need to track down block 5 in layout 7.

Something that gives you a visual cue like the second image would be very helpful.

https://github.com/getkirby/kirby/issues/5453