Merge exid-types.json with gedcom-registries

[tychonievich]

exid-types.json predates gedcom-registries, and has some overlap with it (in particular, it duplicates the semantic purpose of https://github.com/FamilySearch/GEDCOM-registries/tree/main/uri/exid-types). We should merge these two to avoid duplicate information, probably keeping the registries because it is more versatile.