Rustdoc should not render associated items of a negative impl

[dtolnay]

#![feature(negative_impls)]

pub struct Thing;

impl !Iterator for Thing {}

cargo +nightly doc

I would prefer if only the negative impl signature impl !Iterator for Thing were rendered here (and any doc comment on the negative impl). Not even a collapsed-by-default accordion to show the trait's contents. The reader can click the trait's name to see what is in it if they need.

Having associated items of a negative impl rendered is inconvenient because something like CTRL+F for "fn position" will land the reader deep in the middle of the big impl showing them APIs that their type does not have.

Example of this occurring in standard library documentation: impl<'a, I, A: Allocator> !Iterator for &'a Box<[I], A> {}

Mentioning feature(negative_impls) tracking issue. #68318