Show CMake library target in Qt class documentation

Do add a 'CMake target' to the table at the start of class documentations.

 For [QFile|https://doc.qt.io/qt-5/qfile.html,] this might look like

This would allow users to instantly see which target needs to be used in target_link_libraries to make use of the class. The right call to get the target imported should be documented on the module page.