[META] Get rid of #[\AllowDynamicProperties] attribute

Maybe even that parent can be closed now we are hopefully green on PHP 8.2? This issue technically doesn't have to be completed until PHP 9.

Why are we assuming that PHP 9 will deprecate the #[\AllowDynamicProperties] attribute? Is there any official statement about that? I have not seen that.

I think this meta issue is still worth doing, but I'm unclear as to why it's a requirement for either PHP 8.2 or PHP 9.0 compatibility.

> Why are we assuming that PHP 9 will deprecate the #[\AllowDynamicProperties] attribute? Is there any official statement about that? I have not seen that.

I remember seeing something about this being discussed. but that might be outdated. https://wiki.php.net/rfc/deprecate_dynamic_properties explicitly states that this will not be removed, at least that's how I interpret it.

And yes, it's definitely not a PHP 8.2 blocker.

But many of the attributes that we added also cause bad DX (e.g. the undocumented $entity->original property), so in most cases, we do want to get rid of it.

Yeah so far there's no indication that they'll deprecate it, but it doesn't seem impossible that they will, so cutting down the number of places it's used like $entity->original seems good. But we might want to leave it for things like plugin annotations until we actually hear it's going to be deprecated if it's complicated to remove there.

I think I initially misunderstood this attribute as hiding the deprecation in PHP 8.x and that the hard error would occur in PHP 9 either way. But yes for better DX we should declare all properties where possible.