Function parse_trait_assoc_reft

fn parse_trait_assoc_reft(cx: &mut ParseCtxt<'_>) -> ParseResult<TraitAssocReft>

⟨trait_assoc_reft⟩ := fn ⟨ident⟩ ( ⟨refine_param⟩,* ) -> ⟨base_sort⟩ ;?
                    | fn ⟨ident⟩ ( ⟨refine_param⟩,* ) -> ⟨base_sort⟩ ⟨block⟩