Final touches to compile with Qt6

No CI yet though, as this depends on plasma-workspace which still needs
local modifications to build.

host/abstractkrunnerplugin.cpp

@@ -48,7 +48,7 @@ QImage AbstractKRunnerPlugin::imageFromDataUrl(const QString &dataUrl)
         return image;
     }
 
-    const QByteArray b64 = dataUrl.rightRef(dataUrl.count() - b64start - 1).toLatin1();
+    const QByteArray b64 = QStringView(dataUrl).right(dataUrl.count() - b64start - 1).toLatin1();
     const QByteArray data = QByteArray::fromBase64(b64);
 
     if (!image.loadFromData(data)) {

host/mprisplugin.cpp

@@ -525,7 +525,11 @@ void MPrisPlugin::processMetadata(const QJsonObject &data)
         QSize actualSize;
 
         // now parse the size...
+#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
         const auto &sizeParts = sizeString.splitRef(QLatin1Char('x'));
+#else
+        const auto &sizeParts = QStringView(sizeString).split(QLatin1Char('x'));
+#endif
         if (sizeParts.count() == 2) {
             const int width = sizeParts.first().toInt();
             const int height = sizeParts.last().toInt();