macOS: QToolButton/QPushButton menu is "invisible" to VoiceOver

When a QPushButton or a QToolButton have a menu set, and when the button is activated, the menu is ignored by VoiceOver.

Attached is a modified window.cpp from the flowlayout example. To reproduce the issue:

• start VoiceOver
• run the example
• use the tab key to navigate to the button
• press space

The menu will appear, but the VoiceOver focus is still on the button, and there is no "vocal" indication that something happened. Attached is a screenshot of how this looks on screen.

If you hit the down-arrow key now, the first menu item will be selected, but VoiceOver re-reads the assistive text of the button. It looks like the input focus and the VoiceOver focus are off at this point.