Introduce AsField attribute to define field type

[loic425]

With this feature, we'll be able to define custom field types.

As an example:

#[AsField]
final class DateTimeField implements FieldTypeInterface
{
    public function __construct(
        private readonly TwigFieldType $twigFieldType,
    ) {
    }

    public function render(Field $field, $data, array $options): string
    {
        return $this->twigFieldType->render($field, $data, $options);
    }

    public function configureOptions(OptionsResolver $resolver): void
    {
        $this->twigFieldType->configureOptions($resolver);

        $resolver->setDefaults([
            'template' => 'shared/grid/field/datetime.html.twig',
            'vars' => [
                'th_class' => 'w-1 text-center',
            ],
        ]);
    }
}