Add support for usage of placement new together with data model indexes

Two member functions "QAbstractItemModel::createIndex" are described in a terse way. The created model index provides functionality which is similar to a pointer. The technical difference is that a model index is usually viewed as a coordinate which has got the attributes "row" and "column".

Such an index makes an existing object accessible within a data model. Some programmers would prefer to work with pointers (or C++ references) for specific data structures instead.

One C++ programming interface which provides a pointer based on selected input parameters is known as "placement new". How do you think about to use this technique for a direct mapping from position information to a concrete object at more source code places?

I tried to clarify the software situation another bit by the discussion topic "Increasing usage for C++ new operators based on data model indexes?" before.