[9.x] Makes database factories generic

[nunomaduro]

This pull request makes the public methods ( and not protected ) of the database factory class generic. In other words, it allows to get auto-completion like this:

Note that, to get this flavor people need to add this annotation to the top of their existing database factory classes. New database factory classes, created from php artisan make:factory already include this annotation.

/**
 * @extends \Illuminate\Database\Eloquent\Factories\Factory<\App\Models\Team>
 */
class TeamFactory extends Factory
{
    // ..
}

For people who opt for not using this annotation, the auto-completion still works, but on the base model class:

PHPStan wise is still not perfect, as we need the \Illuminate\Database\Eloquent\Model|TModel union is needed to make PHPStorm understand that \Illuminate\Database\Eloquent\Model is the default generic type of TModel.

If this pull request gets merged, I will update the UserFactory class in our skeletons.