Ensure data returned from Intl Enumeration is consistent with data supported by Intl objects

[sffc]

(I remember discussing this before, but I can't find an issue for it)

We should make sure that the lists returned from Intl Enumeration is required by the spec to be the same as the lists of what Intl objects support. For example, Intl.DateTimeFormat should support the calendar systems returned by Intl.supportedValuesOf("calendar"), no more, no less.