Rollup merge of #137956 - compiler-errors:rtn-rustdoc, r=fmease

Add RTN support to rustdoc

This adds support to rustdoc and rustdoc-json for rendering `(..)` RTN (return type notation) style generics.

---

Cleaning `rustc_middle::ty::Ty` is not correct still, though, and ends up rendering a function like:

```rust
pub fn foreign<T: Foreign<bar(..): Send>>()
where
    <T as Foreign>::bar(..): 'static,
    T::bar(..): Sync,
```

Into this:

```rust
pub fn foreign<T>()
where
    T: Foreign,
    impl Future<Output = ()>: Send + 'static + Sync,
```

This is because `clean_middle_ty` doesn't actually have sufficient context about whether the RPITIT is in its "defining scope" or not, so we don't know if the type was originally written like `-> impl Trait` or with RTN like `T::method(..)`.

Partially addresses #123996 (i.e., HIR side, not middle::ty one)

0 files changed, 0 insertions, 0 deletions