Implement localeStringNumber JEXL transformation

Some possibilities:

```
  // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/toLocaleString
  localeStringNumber: (
    n: number,
    locale: Intl.LocalesArgument,
    options: Intl.NumberFormatOptions | undefined,
  ) => n.toLocaleString(locale, options),
```

```
  localeStringNumber: (n, locale, options) => n.toLocaleString(locale, options),
```