{kcm,libkcups}: Add/update logging using ECMQtDeclareLogging tooling
Logging is all over the place here and kcm has none. Let's use the modern tooling, add capability for kcm and update libkcups along the way. Since the widget apps are seeing little to no changes other than clean up, warning fixes and other (hopefully) trivial Qt6 porting mods, leave their logging as is.
Edited by Mike Noe