doctrine:generate:form - Could not load type "date"

# Issue

When creating a form type via `doctrine:generate:form` it creates a line

```
->add('birthday', 'date')
```

which invokes the error

```
Could not load type "date"
```
# Fix proposal

It should create a line

```
->add('birthday', DateType::class)
```

while importing the `DateType`

```
use Symfony\Component\Form\Extension\Core\Type\DateType;
```
