Gui: Qt6 port

* QString::indexOf() is now marked as [[nodiscard]]
* Replace deprecated methods of QMessageBox
* QMouseEvent::globalPos() is deprecated, use globalPosition().toPoint()
* QWidget::enterEvent() requires a QEnterEvent as argument
* QLibraryInfo::location() is deprecated, use path()
* QVariant::Type is deprecated, use QMetaType::Type
* QVariant::canConvert(int) is deprecated, use QVariant::canConvert(QMetaType) or QVariant::canConvert<T>()
* QMessageBox::standardIcon is deprecated, use QStyle::standardIcon()
* Replace deprecated method QMessageBox::question(), ...
* QApplication::fontMetrics() is deprecated
* QDropEvent::mouseButtons() is deprecated, use buttons()
* QDropEvent::keyboardModifiers() is deprecated, use modifiers()
* Constructor of QFontDatabase is deprecated, use static methods instead
* Qt::AA_DisableHighDpiScaling is deprecated
* Qt::AA_EnableHighDpiScaling is deprecated
* Qt::AA_UseHighDpiPixmaps is deprecated

src/Gui/Assistant.cpp

@@ -83,7 +83,11 @@ bool Assistant::startAssistant()
 #elif defined(Q_OS_MAC)
         QString app = QCoreApplication::applicationDirPath() + QDir::separator();
 #else
+#if QT_VERSION < QT_VERSION_CHECK(6,0,0)
         QString app = QLibraryInfo::location(QLibraryInfo::BinariesPath) + QDir::separator();
+#else
+        QString app = QLibraryInfo::path(QLibraryInfo::BinariesPath) + QDir::separator();
+#endif
 #endif
         app += QLatin1String("assistant");