Add test case for transactional DDL

Based on conversation at #4481 it's undesired that consumer should have capabilities to know if they can or cannot run transaction on given DDL. This commit demonstrates that this problem is present in DBAL too and it doesn't handle the case seamlessly. If consumer is not allowed to know if database allows transactional DDL, DBAL should handle attempts to execute DDL within transaction for databases not supporting transactional DDL seamlessly.

tests/Doctrine/Tests/DBAL/Functional/ConnectionTest.php

@@ -8,6 +8,9 @@
 use Doctrine\DBAL\DriverManager;
 use Doctrine\DBAL\ParameterType;
 use Doctrine\DBAL\Platforms\AbstractPlatform;
+use Doctrine\DBAL\Schema\Column;
+use Doctrine\DBAL\Schema\Table;
+use Doctrine\DBAL\Types\Type;
 use Doctrine\DBAL\Types\Types;
 use Doctrine\Tests\DbalFunctionalTestCase;
 use Error;
@@ -283,6 +286,18 @@ public function testTransactionalReturnValue(): void
         self::assertEquals(42, $res);
     }
 
+    public function testTransactionalDDL(): void
+    {
+        $this->connection->transactional(static function (Connection $conn): void {
+            $table = new Table('foo', [new Column('bar', Type::getType('string'))]);
+            foreach ($conn->getDatabasePlatform()->getCreateTableSQL($table) as $sql) {
+                $conn->executeStatement($sql);
+            }
+        });
+
+        self::assertTrue($this->connection->getSchemaManager()->tablesExist('foo'));
+    }
+
     /**
      * Tests that the quote function accepts DBAL and PDO types.
      */