Function hint_iterator 

fn hint_iterator<'db>(
    sema: &Semantics<'db, RootDatabase>,
    famous_defs: &FamousDefs<'_, 'db>,
    ty: &Type<'db>,
) -> Option<(Trait, TypeAlias, Type<'db>)>

Checks if the type is an Iterator from std::iter and returns the iterator trait and the item type of the concrete iterator.