[13.x] Resolve the UsePolicy attribute from parent classes

[xurshudyan]

#[UsePolicy] is only read from the class it's declared on, so a model that extends a base class carrying the attribute resolves no policy at all:

#[UsePolicy(DocumentPolicy::class)]
abstract class Document extends Model
{
}

class Invoice extends Document
{
}

Gate::getPolicyFor(Document::class);   // DocumentPolicy
Gate::getPolicyFor(Invoice::class);   // null
Gate::allows('view', $invoice);       // false — even for an admin