add error for enum

[ying-jeanne]

No description provided.

[sdboyer]

Wow, i can't believe it's been four weeks :/ But, that explains why i've lost so much context on this, and i can't remember a key question: did we agree that this case:

Compose: {
    localstr: LocalEnum | *"bax"
} @cuetsy(kind="interface")

actually should result in an error? If so, i can't remember my reasoning for saying it should, because looking at it now, it seems fine to me that we'd allow either the enum member, or a string, whether in typescript or CUE.