ICE when default method references associated type that can't be normalized

[nikomatsakis]

This trait causes an ICE when implemented and casted appropriately (from #23300):

trait Iterator {
    type Item;

    fn next(&mut self) -> Option<Self::Item>;

    fn cloned(self) -> Cloned<Self> where
        Self: Sized,
        Self::Item: Deref,
        <Self::Item as Deref>::Target: Clone,
    {
        Cloned { it: self }
    }
}

I'll attach the full test in the PR, it's a pain for me to cut-and-paste it right now :)