[kcmkwin/kwindesktop] Use PackageLoader to get effect metadata
Summary:
KPluginInfo(KService::Ptr) is deprecated in favor of using plugin
loaders.
Test Plan:
- Go to System Settins -> Desktop Behavior > Virtual Desktops
- Open Switching tab
- Select Fade desktop
- Click the info button
Reviewers: KWin, apol, davidedmundson
Reviewed By: KWin, davidedmundson
Subscribers: kwin
Tags: KWin
Differential Revision: https://phabricator.kde.org/D13851