[effects/slide] Expose support information

Summary: That's mostly to analyze what options people use in bug reports.

Test Plan:
* Enabled the Slide effect
* Ran `qdbus org.kde.KWin /KWin supportInformation`

Reviewers: #kwin, davidedmundson

Reviewed By: #kwin, davidedmundson

Subscribers: davidedmundson, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D13843