baseFeaturesForEdition function
Returns the fully-resolved BASE FeatureSet for edition before any
file/message/field overrides: the entry's overridable features merged
with its fixed features (fixed wins on conflict). For every supported
edition this yields all six runtime features.
Implementation
Map<String, String> baseFeaturesForEdition(int edition) {
final entry = _defaultsEntryFor(edition);
final result = <String, String>{};
final overridable = entry['overridable'] as Map<String, String>;
final fixed = entry['fixed'] as Map<String, String>;
_putAll(result, overridable);
_putAll(result, fixed);
return result;
}