Use different Object/Ref encoding for virtual methods

[dsnopek]

This attempts to implement option nr 3 from issue #1119

Basically, it just decodes objects from Object ** in virtual methods, and from Object * in all other situations.

There shouldn't affect performance - basically PtrToArg<>::convert() expands to different code when used for a virtual vs non-virtual method.

(It's an alternative to #1123 which is implementing option nr 2)

[saki7]

Thanks for illustrating this solution.

IMHO this approach (option nr 3) should be avoided at all costs because it seems to require a lot of ad-hoc differentiations. Even though we have those helpful if constexpr in our language, it would require same amount of effort on all other bindings. That would become a maintenance burden in future.

Quoting from #1119 (comment):

Given that we're about 1 week passed the feature freeze and Godot PR godotengine/godot#77410 hasn't gotten review from any of the necessary stakeholders, this may end up being the way we need to go for Godot 4.1.

Few hours ago godotengine/godot#77410 has received an approval. We should choose that one alongside with #1123.

[dsnopek]

Superceded by PR #1123