Function getIrregularPlural

getIrregularPlural(singularName: string): string | null
Retrieves the plural form of a word if it is an irregular plural.
Parameters
- singularName: string
  The singular form of the word to check.
Returns string | null
The irregular plural form if found, or null if not found.
Example
```
getIrregularPlural('child'); // returns 'children'
getIrregularPlural('dog'); // returns null
```
- Defined in util.ts:945