port QRegExp to QRegularExpression
As https://doc.qt.io/qt-6/qtcore-changes-qt6.html#regular-expression-classes says:
In Qt 6, the QRegExp type has been retired to the Qt5Compat module and all Qt APIs using it have been removed from other modules. Client code which used it can be ported to use QRegularExpression in its place. As QRegularExpression is present already in Qt 5, this can be done and tested before migration to Qt 6.