- Moved Variant struct definition to its own file so it can be used
without include cycles (like on Dictionary).
- Add `index` operator function so bindings like C++ can implement the
operator[] overload (which needs a reference to the actual value).
- Added missing new/destroy functions to Vector3i array.
- Added print error/warning functions as helpers so bindings can print
messages in the same manner as Godot itself does.
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