Make commandbar a normal widget instead of a window
Commandbar never really needed to be a window on its own because it was always inside the parent widget. So far it has worked okay but it has some issues on other platforms like not being able to paste text in the QLineEdit on macOS.
This change makes the command bar a normal widget that is completely handled by Qt. This has many advantages: -> Same behaviour on all platforms -> Application shortcuts now work from inside the command bar, this allows us to jump between various commandbar like widgets in Kate directly. -> faster to open