Adjust KeyboardLayout to non-kded DBus service

Summary:
The keyboard layout kded module does also register a dedicated DBus
service and a dedicated object. By using the newer service name we
can also provide the same on Wayland where there is no kded module
for keyboard.

Test Plan: Not yet tested as I'm on Wayland

Reviewers: #plasma_on_wayland

Subscribers: plasma-devel

Tags: #plasma_on_wayland

Differential Revision: https://phabricator.kde.org/D4322