6154: Shorten type hints for std::iter Iterators r=SomeoneToIgnore a=Veykril
Fixes#3750.
This re-exports the `hir_expand::name::known` module to be able to fetch the `Iterator` and `iter` names.
I'm not sure if there is anything to do with `Solution::Ambig` in `normalize_trait_assoc_type` or whether discarding those results is always wanted.
Co-authored-by: Lukas Wirth <lukastw97@gmail.com>