Rollup merge of #102439 - fmease:rustdoc-simplify-cross-crate-trait-bounds, r=GuillaumeGomez

rustdoc: re-sugar more cross-crate trait bounds

Previously, we would only ever re-sugar cross-crate predicates like `Type: Trait, <Type as Trait>::Name == Rhs` to `Type: Trait<Name = Rhs>` if the `Type` was a generic parameter like `Self` or `T`. With this PR, `Type` can be any type.

Most notably, this means that we now re-sugar predicates involving associated types (where `Type` is of the form `Self::Name`) which are then picked up by the pre-existing logic that re-sugars them into bounds. As a result of that, the associated type `IntoIter` of `std`'s `IntoIterator` trait (re-exported from `core`) is no longer rendered as:

```rust
type IntoIter: Iterator
where
    <Self::IntoIter as Iterator>::Item == Self::Item;
```

but as one would expect: `type IntoIter: Iterator<Item = Self::Item>;`.

Cross-crate closure bounds like `F: Fn(i32) -> bool` are now also rendered properly (previously, the return type (`Self::Output`) would not be rendered and we would show the underlying equality predicate).

Fixes #77763.
Fixes #84579.
Fixes #102142.

`@rustbot` label T-rustdoc A-cross-crate-reexports
r? rustdoc

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