Debug assert that parsed attributes are in the `BUILTIN_ATTRIBUTE_MAP` There are currently two sources of truth for which attributes are builtin, the `BUILTIN_ATTRIBUTE_MAP` and the list of parsers. The long term goal is to get rid of the `BUILTIN_ATTRIBUTE_MAP` , but because of the way that crates depend on eachother this is not trivial. This PR makes sure the sources don't diverge. r? @mejrs