fix(kcm): show output ids in reference to currently applied config

Summary:
Currently output identification uses the pending configuration to position
output ids. That can result in output ids being inverted (if you move screen
for example).

In order to fix that, we instead use the applied configuration to identify
outputs.

Reviewers: Plasma, romangg

Reviewed By: Plasma, romangg

Subscribers: romangg, davidedmundson, plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D28818