There was no need to use FlyString for error messages, and it just
caused a bunch of churn since these strings typically only existed
during the lifetime of the error.
The spec isn't _super_ clear on how this is meant to be done, but the
way I understand this is that we should simply clamp the returned
'current value' between 'min' and 'max'.
Firefox does not appear to do this clamping, but Chrome does.
