Function catalogUsage

catalogUsage(
catalog: Catalog,
referencedKeys: Iterable<string>,
): CatalogUsageStats
Which of a catalog's keys a game's own source actually references, and which just sit there. mwg has no idea how a game's code names a message key (a string literal, a generated constant, a SemanticMessage.type) - referencedKeys is however the caller already found that out (typically a grep or a build-time scan over its own source), the same boundary rollRoster draws around a game's own roster values.
Parameters
- catalog: Catalog
- referencedKeys: Iterable<string>
Returns CatalogUsageStats
Example
```
import { catalogUsage } from '@datamoc/mw_games/i18n';

const catalog = {
  locale: 'en', direction: 'ltr' as const,
  messages: { greeting: 'Hi', unused: 'never shown' },
};

catalogUsage(catalog, ['greeting']); // { totalKeys: 2, usedKeys: 1, unusedKeys: ['unused'] }
```
- Defined in src/i18n/Content.ts:144