message: starlark: derive: make macros a little more qualified
  Summary:
  Accessing `Frozen` on a struct requires that the only trait it implements with
  an associated type called `Frozen` is `Freeze`, which isn't guaranteed to work,
  but also isn't entirely necessary.
diff: @@ -52,7 +52,7 @@ impl<'a> Input<'a> {
  #name
  });
  output_params.push(quote! {
  - #name::Frozen
  + <#name as starlark::values::Freeze>::Frozen
  });
  }
  GenericParam::Lifetime(lt) => {
  