New combined data struct for IANA name mapping

[sffc]

Split from #4548

This new data struct supports all operations, some faster than others:

1. IANA-to-BCP47 is a fast O(1) trie lookup
2. IANA Normalization is also a fast O(1) trie lookup
3. BCP47-to-IANA requires an O(N) traversal over the trie
4. IANA Canonicalization is O(1) if the ID is already canonical, and falls back to BCP47-to-IANA if not canonical

I think we should keep Bcp47ToIanaMapV1 around for users who want O(1) performance in all cases and don't mind paying the extra data size cost.

I split this from #4548 because I want to work more on the API but want to get the data provider side of my work checked-in.