Fix toolbuttons with menus using newer Breeze
Now that Breeze has a toolbutton-with-instant-menu style, clean up the things needed for Kirigami to use it. This involves removing some extra spacing, making sure we do not set AutoRaise for non-flat buttons and exposing the menu property as an actual property on the background. The last one is done because setting a property on the properties map breaks all bindings.
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