Issues with QStyleOptionMenuItem settings when passed to QStyle for QtQuickControls

See https://bugs.kde.org/show_bug.cgi?id=339106

When QStyleOptionMenuItem settings are passed to QStyle for rendering QtQuick Controls, some values are not set poperly (that is, inconsistent with what is passed from QWidgets):

maxIconSize is always set to zero, even if some menu items actually have icons (with non zero size)
menuHasCheckableItems is always set to true even if no menu items are checkable

As a consequence
1/ the style has to ressort to a fixed icon size (PM_SmallIconSize) to allocate the space needed for items,
2/ and always add the necessary space for checkable items even if none exists.

This results in unnecessary blank space when all items in the menu have no icons, nor checkboxes.