[libkwineffects] Port the remaining bits of API to dynamic dispatch

Summary:
7834bec5 missed to port minimize and
unminimize to dynamic dispatch. In addition to that, we don't benefit
from QMetaObject::invokeMethod so port addRepaint and addLayerRepaint
to dynamic dispatch as well.

Reviewers: #kwin, davidedmundson

Reviewed By: #kwin, davidedmundson

Subscribers: davidedmundson, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D18049