message: Make conversion of starlark Value to CommandLineLike use FrozenRef
diff: @@ -544,6 +544,13 @@ impl FrozenValue {
  .downcast_ref::<T>()
  .map(|t| FrozenRef { value: t })
  }
  +
  + /// Note: see docs about ['Value::unpack_box_str'] about instability
  + pub fn downcast_frozen_str(self) -> Option<FrozenRef<Box<str>>> {
  + self.to_value().unpack_box_str().map(|s| FrozenRef {
  + value: unsafe { transmute!(&Box<str>, &'static Box<str>, s) },
  + })
  + }
  }
  mod std_traits {
  