Can structured headers' <ins>/<del> UI be improved?

[justingrant]

The fix in #533 enables <ins class="block"> and <del class="block"> to be used for the entire H1 of a structured header. This is an improvement, thanks! However:

• The changes aren't represented in the left-hand table of contents pane, unlike <ins>/<del> used in unstructured headers
• Deleted text is shown verbatim, in a huge H1 font, which is distracting for long parameter lists or long return type text. It also makes it harder to determine what actually has changed, because return types and parameter types are displayed differently (and far away from each other) in the <ins> block vs. the <del> block

Ideally, I'd be able to get the same reader-facing UI I can get with unstructured headers, which is that I can revise the AO name, a parameter name, a parameter type, and/or a return type, and only the changed parts would be shown in red or green background.

The screenshot below shows both problems, and shows examples in the left pane of unstructured headers' UI providing the desired behavior.

[justingrant]

In case it's helpful, https://github.com/tc39/ecmarkup/pull/533#issuecomment-1611710276 includes an idea from @gibson042 for how to support more granular <ins> and <del>.