QMenu: Change multiple checkable items without closing the menu

It should be possible to toggle checkable options (or select multiple exclusive options) in a QMenu, without having to reopen it after each change.

Using keyboard: Press "Space" instead of "Enter" on an option.
Using mouse: Shift+Click or Middle-Click on an option.

This was requested for KDE, but should be resolved on a Qt level.

https://bugs.kde.org/show_bug.cgi?id=180814