Declare operator| for QFlags in namespace of corresponding class
This is recommended in modern C++ and doesn't cause weird build problems anymore since Qt 5.12. (see https://codereview.qt-project.org/c/qt/qtbase/+/225348)
This is recommended in modern C++ and doesn't cause weird build problems anymore since Qt 5.12. (see https://codereview.qt-project.org/c/qt/qtbase/+/225348)