Add a setting to keep normal notifications always on top
Fixes https://bugs.kde.org/show_bug.cgi?id=425071.
In discussion there Nate said that it's fine to reuse PlasmaCore.Dialog.CriticalNotification
type for normal notifications, if user wants them to show up on top.
I thought that such change wouldn't really be convenient for most users, as notifications over fullscreen windows wouldn't time out (because they would be considered critical), so I didn't try to make this into a proper patch. But while using it I found out that such notifications do actually time out. I guess that the thing that is responsible for timing them out looks at the urgency, not the type, which is really convenient. So I went ahead and tried to make this into a proper patch that hopefully can be accepted in upstream.
There also will be a pretty straightforward companion MR to plasma-desktop
, to add this setting into UI.