"Pick Screen Color" from non-native QColorDialog is not working on Mac

"Pick Screen Color" from non-native QColorDialog is not working on Mac.

Steps to reproduce:

• Take "Standard Dialogs Example" from Qt examples
• Build it with 5.12 Qt version
• Try to use "Pick Screen Color" from non-native QColorDialog
  Actual: Unable to use the tool even inside the dialog it-self. It shows and picks incorrect color.
  Expected: "Pick Screen Color" shows and picks correct color inside the dialog and outside of it.

Note: with Qt 5.6 libs QColorDialog has behavior inside the dialog but incorrect outside of it.

Dirty Workaround: Use QTimer with QCursor::pos() for making QEvent::MouseMove for the dialog. And Objective-C++ with Native watcher for catching mysterious NSEvent(NSSystemDefined) for posting QEvent::MouseButtonRelease event.