Adds qt migration example

qt5-before/qt5-legacy-migration-benchmark/main.cpp

@@ -0,0 +1,16 @@
+#include <QApplication>
+#include <QTextCodec>
+#include "MainWindow.h"
+
+int main(int argc, char *argv[])
+{
+#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
+    QTextCodec::setCodecForLocale(QTextCodec::codecForName("UTF-8"));
+#endif
+
+    QApplication a(argc, argv);
+    MainWindow w;
+    w.show();
+
+    return a.exec();
+}