cxx-qt-lib: Can we use C++ templates to reduce the amount of C++ code

[LeonMatthes]

The most common C++ functions we need for cxx-qt-lib are:

• Various constructors (default, copy, etc.)
• Destructor

So could we just add a "cxx-qt-lib/common-utils.h" that defines templates for these.
e.g. for the destructor:

template<class T>
void destruct(T &t) {
    t.~T();
}

We've already found that CXX can deal with this pretty well, as long as it can infer all template type arguments.

[ahayzen-kdab]

We think yes as this already is done with QSet<T>.