Transfer: implement 'Grab QR code from screen' functionality

src/qt/macoshelper.h

@@ -29,6 +29,8 @@
 #ifndef MACOSHELPER_H
 #define MACOSHELPER_H
 
+#include <QPixmap>
+
 class MacOSHelper
 {
     MacOSHelper() {}
@@ -36,6 +38,7 @@ class MacOSHelper
 public:
     static bool isCapsLock();
     static bool openFolderAndSelectItem(const QUrl &path);
+    static QPixmap screenshot();
     static QString bundlePath();
 };