This introduces a similar change to kiod5 that was already made to other comparable background applications:

1 the LSUIElement InfoDict key is set, causing the application to run like an "agent" (without Dock or AppSwitcher presence)
2 in case of kiod5, this state has to be confirmed just before calling QApplication::exec() (failure to do so disables text inputs in the dialogs the application may post)
3 when a password dialog is posted the application (kiod5) is brought to the foreground instead of attaching the dialog to the application responsible for the request.

works as intended on Mac, no change elsewhere.

It might be useful to include the functions used in 1) and 2) above in KWindowSystem to avoid unnecessary duplication (and having to introduce ditto ObjC files).