Add support for Symfony Country Constraint

manual test case:
1) add a Country constraint to field_test, alpha3 uncheck, save it.

if populate field_test "123456", get an error message.

if populate field_test "CN", no error message.

2) if change alpha3 checked,

if populate field_test "123456", get an error message.

if populate field_test "CN", get an error message.
if populate field_test "CHN", no error message.

Note:
You need install symfony/intl and PHP's intl extension, to make this constraint works.
composer require symfony/intl

Automatically closed - issue fixed for 2 weeks with no activity.

This change broke my D10 upgrade.

There is a compatibility issue with the address contrib module → , in the AddressItem field type they are decraring a "Country" constraint and giving a "availableCountries" option which they collide with this change and provoking the following error :

Symfony\Component\Validator\Exception\InvalidOptionsException: The options "availableCountries" do not exist in constraint "Drupal\field_validation\Plugin\Validation\Constraint\CountryConstraint". in Symfony\Component\Validator\Constraint->normalizeOptions() (line 180 of /app/vendor/symfony/validator/Constraint.php).

I think we should find another id for the CountryConstraint.