[5.4] Add raw method to FactoryBuilder

[jerguslejko]

This PR adds raw() method to Illuminate\Database\Eloquent\FactoryBuilder.

It allows for calling factory(User::class)->raw() which returns raw attributes array (merged with overrides). raw() method behaves in a same way as make() or create() methods do.

It aligns nicely with Illuminate\Database\Eloquent\Factory::raw() method which is available inside factories.

This feature is useful when writing tests for a simple endpoint:

function it_creates_an_order()
{
    $request = factory(App\Order::class)->make()->toArray();

    // vs

    $request = factory(App\Order::class)->raw();

    $this->post('/orders', $request);
}

Also, it could be used with hasMany relationships:

$post->comments()->create(
    factory(App\Comment::class, 3)->raw()
);

🌵