Padding properties exists as reserved properties but don't have effect.
But the menu code was using them to store values.
This is now a warning because people got confused by setting padding and
wondering why it has not effect.
This also had some bug in the code were properties were padding was set
on a layout, as well as all the padding-* properties, so the padding was
not taking in account
This adds an icon that is displayed to the left of the title, and is
also shown for Menus are inside of a parent menu.
Closes#7791
ChangeLog: Added icon property to MenuItem and Menu
By default it's enabled, of course. This property is not only added to
MenuItem, but Menu as well - since they can be nested. It's also
possible to select a disabled item, but it's hard to modify that since
it's logic is written in Slint. You should be prevented from activating
it with a tap or key press at least.
See #7791
