[transform] Implement contracts: Doesn't work with abstract parent implementig interfaces

e.g. 

```
class VoucherStep extends AbstractBaseStep
```

Where `AbstractBaseStep`:

```
use Spryker\Yves\StepEngine\Dependency\Step\AbstractBaseStep as SprykerBaseStep;
abstract class AbstractBaseStep extends SprykerBaseStep
```

and

```
abstract class AbstractBaseStep implements StepInterface
```