[Validator] Hint that egulias/email-validator needs to be installed for strict mode as default config

Author: mpdude

Constraints/EmailValidator.php

@@ -100,6 +100,10 @@ public function validate($value, Constraint $constraint)
         }
 
         if (null === $constraint->mode) {
+            if (Email::VALIDATION_MODE_STRICT === $this->defaultMode && !class_exists(EguliasEmailValidator::class)) {
+                throw new LogicException(sprintf('The "egulias/email-validator" component is required to make the "%s" constraint default to strict mode.', EguliasEmailValidator::class));
+            }
+
             $constraint->mode = $this->defaultMode;
         }