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

@@ -36,7 +36,7 @@
 #include <QSslSocket>
 #include <QVideoSink>
 
-#include "zxing-cpp/example/ZXingQtReader.h"
+#include "../3rdparty/zxing-cpp/example/ZXingQtReader.h"
 
 using namespace ZXingQt;