Cast properties with self or parent type

[sebdesign]

This PR fixes a bug when a type property has the self or parent keyword.

Here is a simple example with a nullable self property:

class MyDTO extends DataTransferObject
{
    public string $name;
    public ?self $parent;
}

$dto = new MyDTO([
    'name' => 'a',
    'parent' => ['name' => 'b'],
]);

// TypeError: Cannot assign array to property MyDTO::$parent of type ?self
// vendor/spatie/data-transfer-object/src/Reflection/DataTransferObjectProperty.php:47
// vendor/spatie/data-transfer-object/src/DataTransferObject.php:29

The same applies for the parent keyword.

The reason is that the DataTransferObjectProperty cannot resolve the caster (e.g. DataTransferObjectCaster) for the property, because resolveCasterFromType() returns an empty array.
This happens because $type->getName() returns self so class_exists('self') is false.
In order to fix, this I'm parsing the type name and resolving the self and parent keywords to the concrete classes.

[brendt]

Looking good, thanks!

[brendt]

Tagged: https://github.com/spatie/data-transfer-object/releases/tag/3.7.1