isClassifiedYamlKey function
Whether key is classified: owned by a SharedSetting or documented
as file-only. The completeness gate (test/parity/
settings_completeness_test.dart) fails on any parsed key where this is
false.
Implementation
bool isClassifiedYamlKey(String key) =>
settingForYamlKey(key) != null || fileOnlyConfigKeys.containsKey(key);