Pass TRANSIENT_INACTIVE flag for windows with WA_ShowWithoutActivating

When setting a transient window also evaluate the state of the window
attribute WA_ShowWithoutActivating. If that flag is set the transient
should get the inactive flag as well.

Task-number: QTBUG-55403
Change-Id: I757e5527e78f730a440e26abb52e84c9b2bb2f3a
Reviewed-by: Johan Helsing <johan.helsing@qt.io>
Reviewed-by: Giulio Camuffo <giulio.camuffo@kdab.com>