LibJS+LibUnicode: Parse Unicode keywords from the BCP 47 CLDR package

We have a fair amount of hard-coded keywords / aliases that can now be
replaced with real data from BCP 47. As a result, the also changes the
awkward way we were previously generating keys. Before, we were more or
less generating keywords as a CSV list of keys, e.g. for the "nu" key,
we'd generate "latn,arab,grek" (ordered by locale preference). Then at
runtime, we'd split on the comma. We now just generate spans of keywords
directly.

Userland/Libraries/LibJS/Runtime/Intl/AbstractOperations.cpp

@@ -427,7 +427,7 @@ LocaleResult resolve_locale(Vector<String> const& requested_locales, LocaleOptio
         // b. Assert: Type(foundLocaleData) is Record.
         // c. Let keyLocaleData be foundLocaleData.[[<key>]].
         // d. Assert: Type(keyLocaleData) is List.
-        auto key_locale_data = Unicode::get_locale_key_mapping_list(found_locale, key);
+        auto key_locale_data = Unicode::get_keywords_for_locale(found_locale, key);
 
         // e. Let value be keyLocaleData[0].
         // f. Assert: Type(value) is either String or Null.