[JSON:API] Add toAttributes() method

[crynobone]

This is an improvements to #57571 and allows using toAttributes() method or $attributes property whenever possible.

Using property

class UserResource extends JsonApiResource
{
    protected $attributes = [
        'name',
        'email',
    ];
}

Using method

class UserResource extends JsonApiResource
{
    public function toAttributes(Request $request)
    {
        return [
            'name',
            'email',
            'avatar' => url("/images/profile/{$this->id}.png"),
        ];
}