[AddressingBundle] The collection form type uses the new CollectionExtension

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Behat?    | Almost
| Phpspec? | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

Here and in other places you can simplify that code to:
```php
$collectionSelector = $collectionSelector ?: $this->getDefaultCollectionSelector();