higher-ranked `dyn Trait`, fn pointers, and closures allow normalizing to non-wf type

trait Trait<'hr> {
    type Assoc;
}

struct W<T, U>(T, U);
trait Extend<'a, 'b> {
    fn extend(x: &'b str) -> &'a str;
}
impl<'a, 'hr, 'b> Extend<'a, 'b> for W<&'a &'hr (), &'hr &'b ()> {
    fn extend(x: &'b str) -> &'a str {
        x
    }
}

fn extend_via_dyn<'a, 'b, T: for<'hr> Trait<'hr, Assoc: Extend<'a, 'b>> + ?Sized>(x: &'b str) -> &'a str {
    T::Assoc::extend(x)
}

fn extend<'b>(x: &'b str) -> &'static str {
    extend_via_dyn::<dyn for<'hr> Trait<'hr, Assoc = W<&'static &'hr (), &'hr &'b ()>>>(x)
}

fn main() {
    let x = extend(String::from("temp").as_str());
    println!("{x}");
}

The underlying issue has been discovered by @theemathas in https://github.com/rust-lang/rust/issues/152467#issuecomment-3882205618.

Start by compiling the reproducer in the issue and reading the discussion in issue #152467. Investigate how higher-ranked dyn Trait associated-type normalization interacts with function pointers and closures. Done means the compiler no longer permits the shown program to normalize to a non-well-formed type.