getCountryCities function
Get the list of cities that belongs to a country by the country ISO CODE
Implementation
Future<List<City>> getCountryCities(String countryCode) async {
final cities = await _loadCities();
final res = cities.where((city) {
return city.countryCode == countryCode;
}).toList();
res.sort((a, b) => a.name.compareTo(b.name));
return res;
}