Fix ownership of the content of Variant

Copy and move of Variants holding Array2D, LabeledArray or string array
values copied the storage byte by byte, so copies shared the same heap
buffers, and the destructor never destroyed these objects, leaking them.
Assignments never released the previous content, move assignment of
strings and arrays duplicated the buffer and dropped the original one,
and move assignment of string arrays corrupted the source vector.

Author: aalkin

Framework/Core/include/Framework/Variant.h

@@ -403,6 +403,7 @@ class Variant
     *this = Variant(value, size);
   }
 
+  /// FIXME: set for vector of strings is not used anywhere, why?
   template <typename T>
   void set(std::vector<T>& values)
     requires(std::is_pod_v<T> || std::is_same_v<T, std::string>)