kstyle: Draw KIconButton as icon with edit overlay

Otherwise it's just a non-descript button with an icon. Adding an edit overlay makes it clear that this thing can be used to edit the icon.

kstyle: Add _breeze_round_button property for drawing circular buttons

This is used in Qt Quick for example for edit overlays. With this, something similar can be used in Qt Widgets.

---

Used by frameworks/kiconthemes!185 (merged)

Below a certain size (when the button would just cover the icon) it’s rendered as a regular push button as before.

File properties dialog:

Edit places entry:

File type editor: