Change _can_handle and _edit virtual methods to take Object*

[Zylann]

Not sure why they were taking Variant while it's always been for Objects and other related virtual methods take Object* already.

[akien-mga]

This changes the behavior, no? How does this affect existing plugins and the actual reference counting on that resource?

[Zylann]

I dont think it is supposed to change behavior, it's passed just the same as every other virtual method taking Object* already. If reference count has to increase, it will happen in the callee.

[mhilbrunner]

cc @reduz you changed this in #51970

[reduz]

The reason it takes Variant is because, if you are editing a Ref<> type, it properly passes the reference counter. If you pass a pointer, you may miss it until you re assign it to something. Not sure if in practice it makes any difference.

[Zylann]

My understanding is that it really makes no practical difference because in every case if the callee wants to store it, it should be using a Ref<T> or Variant anyways. If the callee stores the pointer without checking the reference case, that's a mistake of the callee. Also, there are other places where the API takes Object* already, and in Godot modules it always takes Object*. So it is at least inconsistent, which is why I made this PR.

[RandomShaper]

This is fine. RefCounted object's reference count is respected through the GDVIRTUAL_CALL(). Using Variant was incrementing it to later decrement back on return, which didn't really add any value (maybe in past codebases that had a role?). Moreover, if the call chain required the cast, handles() would already be in trouble. I agree with @Zylann in that the callee is the responsible for keeping the object referenced if it needs to. In any case, doing the cast wasn't really woking as a safety measure, preventing a failure to do so from causing trouble.

[akien-mga]

@Zylann Could you rebase this PR?

Edit: Did it myself to be able to merge this today.

[akien-mga]

Thanks!