QDS-11412 Implement built-in QR code reader

This MR brings the following features;

• add: built-in QR code reader based on zxing-cpp library
• chore: bump to Qt 6.6.1 to fix camera access issues (QTBUG-116526)

src/backend.cpp

@@ -112,15 +112,6 @@ void Backend::updateInBackground(const bool &enabled)
 
 void Backend::scanQrCode()
 {
-    // camera settings
-    // for (const QCameraFormat &fmt : QMediaDevices::videoInputs().at(0).videoFormats()) {
-    //     qDebug() << "======================";
-    //     qDebug() << "max framerate:" << fmt.maxFrameRate();
-    //     qDebug() << "min framerate:" << fmt.minFrameRate();
-    //     qDebug() << "pix fmt:" << fmt.pixelFormat();
-    //     qDebug() << "res:" << fmt.resolution();
-    // }
-
     m_captureSession.reset(new QMediaCaptureSession(this));
     m_captureSession->setCamera(new QCamera(this));
     m_captureSession->setVideoOutput(new CustomVideoWidget);