This in the scope of a duplication triggered via any type in the `Variant` realm. that is, the following: `Variant` itself, `Array` and `Dictionary`. That includes invoking `duplicate()` from scripts.
A `duplicate_deep(deep_subresources_mode)` method is added to `Variant`, `Array` and `Dictionary` (for compatibility reasons, simply adding an extra parameter was not possible). The default value for it is `RESOURCE_DEEP_DUPLICATE_NONE`, which is like calling `duplicate(true)`.
Remarks:
- The results of copying resources via those `Variant` types are exactly the same as if the copy were initiated from the `Resource` type at C++.
- In order to keep some separation between `Variant` and the higher-level animal which is `Resource`, `Variant` still contains the original code for that, so it's self-sufficient unless there's a `Resource` involved. Once the deep copy finds a `Resource` that has to be copied according to the duplication parameters, the algorithm invokes the `Resource` duplication machinery. When the stack is unwind back to a nesting level `Variant` can handle, `Variant` duplication logic keeps functioning.
While that is good from a responsibility separation standpoint, that would have a caveat: `Variant` would not be aware of the mapping between original and duplicate subresources and so wouldn't be able to keep preventing multiple duplicates.
To avoid that, this commit also introduces a wormwhole, a sharing mechanism by which `Variant` and `Resource` can collaborate in managing the lifetime of the original-to-duplicates map. The user-visible benefit is that the overduplicate prevention works as broadly as the whole `Variant` entity being copied, including all nesting levels, regardless how disconnected the data members containing resources may be across al the nesting levels. In other words, despite the aforementioned division of duties between `Variant` and `Resource` duplication logic, the duplicates map is shared among them. It's created when first finding a `Resource` and, however how deep the copy was working at that point, the map kept alive unitl the stack is unwind to the root user call, until the first step of the recursion.
Thanks to that common map of duplicates, this commit is able to fix the issue that `Resource::duplicate_for_local_scene()` used to ignore overridden duplicate logic.
