[10.x] Make ComponentAttributeBag JsonSerializable

[iamgergo]

Currently it is not possible to automatically convert to array or JSON serialize the ComponentAttributeBag, but in some cases it would be handy.

json_encode(['attributes' => new ComponentAttributeBag(['class' => 'form-control'])]);

// {"attributes":{}}

We can use (new ComponentAttributeBag(['class' => 'form-control']))->getAttributes(), but it would be a better DX to handle this automatically, in my opinion.