Ensure that the provider performs correct Norwegian macrolanguage fallback

[hsivonen]

Ensure that requesting the collation for nn or nb loads the collation for no. (Also check nn-NO and nb-NO to see that ignoring more specific but irrelevant tags works in the context of macrolanguage fallback.)

[hsivonen]

CC @sffc

[hsivonen]

The macrolanguage fallback isn't in CLDR's collation files but assumes knowledge of the Macrolanguage: field in the language subtag registry.

[hsivonen]

There are other macrolanguage relationships in the language subtag registry that fall back to languages with non-root collations, particularly ar and sq. OTOH, the relationship between Serbian, Bosnian, and Croatian collations is handled by a combination of imports and aliases in CLDR.

[sffc]

The nn/nb/no mappings are in the CLDR parent locales:

• https://github.com/unicode-org/icu4x/blob/main/provider/testdata/data/cldr/cldr-core/supplemental/parentLocales.json

So this should work by default (as soon as the rest of #1109 is fully implemented). I will add a test specific for collator and then close this issue.