Email validation allows deprecated email addresses

Problem/Motivation

In some rare cases users accidentally(?) enter a space immediately before the @ sign in email addresses. This is RFC-compliant, but deprecated and triggers a warning in Egulias\EmailValidator\Validation\RFCValidation->isValid.

So an email address like this would be valid, but most servers do not handle it, triggering an error error while sending the mail:

mmbk @example.org

Steps to reproduce

1. Use any form that has an email field (for example the /admin/config/system/symfony-mailer-lite/test )
2. Enter an address containing a space before the "at" sign, like mmbk @example.org
3. The mail transfer will fail

(sorry for the german screenshot )

Proposed resolution

egulias/email-validator supports another validator NoRFCWarningsValidation that is doing the same validations and treats the warnings as errors, so a mail like this cannot be entered.

Remaining tasks

Basically the change is:

diff --git a/lib/Drupal/Component/Utility/EmailValidator.php b/lib/Drupal/Component/Utility/EmailValidator.php
index f1345d03b1..f86efa7411 100644
--- a/lib/Drupal/Component/Utility/EmailValidator.php
+++ b/lib/Drupal/Component/Utility/EmailValidator.php
@@ -4,7 +4,7 @@ namespace Drupal\Component\Utility;
 
 use Egulias\EmailValidator\EmailValidator as EmailValidatorUtility;
 use Egulias\EmailValidator\Validation\EmailValidation;
-use Egulias\EmailValidator\Validation\RFCValidation;
+use Egulias\EmailValidator\Validation\NoRFCWarningsValidation;
 
 /**
  * Validates email addresses.
@@ -27,7 +27,7 @@ class EmailValidator extends EmailValidatorUtility implements EmailValidatorInte
     if ($email_validation) {
       throw new \BadMethodCallException('Calling \Drupal\Component\Utility\EmailValidator::isValid() with the second argument is not supported. See https://www.drupal.org/node/2997196');
     }
-    return parent::isValid($email, (new RFCValidation()));
+    return parent::isValid($email, (new NoRFCWarningsValidation()));
   }
 
 }

User interface changes

NONE

Introduced terminology

NONE

API changes

NONE

Data model changes

NONE