rustdoc: reexports of hidden items are not hidden, and look confusing

I tried searching for the (unstable) Receiver trait in the standard library. The only result it links to is this:

I would expect this to be clickable or have some other way for me to look at the actual definition of this trait. But nothing, the story just ends here.

Looking at the trait, I noticed this:

#[doc(hidden)]
pub trait Receiver {
    // Empty.
}

So probably the doc(hidden) is why we don't get a link. But shouldn't rustdoc then also hide the reexport?

Start by reproducing the standard-library search for Receiver and inspect rustdoc's handling of the #[doc(hidden)] trait and its reexport.Receiver entry. Done means the generated documentation no longer exposes a non-clickable reexport for the hidden item, with a regression check for this case.