gtk4: wf-panel menu widget logout default UI is not the same as the gtk3 version

[soreau]

The logout dialog when clicking on logout button in gtk4 wf-panel menu widget could use some work. I think the target goal should be to mimic the gtk3 wf-panel menu widget logout dialog as closely as possible.

[soreau]

Things look much better since recent commits but there is still no window around the buttons, at least here.