Draw arrows on toolbuttons with menus and no popup delay

While working to make the desktop style responsible for tool button drawing in Kirigami, we found out that Breeze lacks any indicator when there's a menu attached to a tool button that is instant popup. This changes tool buttons to draw a downward pointing arrow when they have a menu. This makes them match the behaviour of push buttons and also of earlier versions of Kirigami. The exception is tool buttons that show only an icon, which are currently not changed. This is because they are often used for overflow or application menus and similar roles, which already indicate they are menus and there is no real nice way of determining which role the tool button is used for.

See also https://bugs.kde.org/show_bug.cgi?id=344746

	Before	After
oxygen-demo5
dolphin

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