Make PDO transaction methods throw PDOException&DriverException

[maxm86545]

Fixes to match \Doctrine\DBAL\Driver\Connection: beginTransaction, commit and rollBack must throw \Doctrine\DBAL\Driver\Exception. For backwards compatibility \PDOException has been keep for version 3.*. Replace #5886

Previous behavior:

try {
   $connection->beginTransaction();
} catch(\PDOException) {
  // The code can be executed
}

try {
   $connection->beginTransaction();
} catch(\Doctrine\DBAL\Driver\Exception) {
  // The code will never be executed :(
}

Current behavior:

try {
   $connection->beginTransaction();
} catch(\PDOException) {
  // The code can be executed
}

try {
   $connection->beginTransaction();
} catch(\Doctrine\DBAL\Driver\Exception) {
  // The code can be executed :)
}

[derrabus]

Oh, now I get what you're doing here. Yeah, that might work. Will have a closer look later. Thanks for the PR.