[REG 5.8 -> 5.9] Windows: When showing a menu of app on secondary screen in HighRes/LowRes multimonitor setup with HighDpiScaling active, app gets stuck moving the menu between screens

This seems to be a regression in Qt. Unfortunately I could not reproduce it with a simple example so I hope you can add the details and forward the issue.

1. Have a primary UHD-screen scaled to 200% and a secondary FullHD-screen scaled to 100%.
2. Run Creator on the secondary screen.
3. Open a file in Creator.
   I tried C++ and QML files.
4. Right-click into the file.
   You'll see something wobbling where the menu should be but it won't show up correctly.

With a Creator built on Qt 5.7.1, this works correctly.