rustdoc ui doesn't show associated types for folded summaries of trait implementations

For traits like Iterator or Future, it's essential to know what is their associated type. However, lists of trait implementations can be folded into a summary, and the summary hides the associated type.

The detailed list of trait implementations for a type can be quite long, so it's easier to scan it with all items folded into summaries (using top-right summary button). That makes the trait implementations also less informative:

I think the summaries could be made more useful by including the associated type in the summary somehow:

impl Iterator for Foo // Item = Bar

and the redundant annotation can be hidden when the details are expanded, with a bit of CSS trickery:

<style>
    details[open] > summary span {
        display: none;
    }
</style>
<details>
    <summary>impl Iterator for Foo <span>// Item = Bar</span></summary>
    type Item = Bar
</details>

Start by locating the rustdoc UI code that builds folded summaries for trait implementations and inspect how associated types are rendered in the expanded details. Add the associated type to folded summaries while keeping the expanded view free of redundant text, then verify the resulting HTML and styling against the Iterator or Future example described in the issue.