Alberts Muktupāvels authored Mar 18, 2022 and Marco Trevisan committed Sep 16, 2022

- Set button always sets new icon. This should emit icon-changed
signal unless there is higher priority icon already set.

- Nochange button is used to cause PropertyNotify event that should
not cause changes to icon and/or should not emit icon-changed
signal.

- Unset button is used to remove icon. This should emit icon-changed
signal only if highest priority icon is unset.