Paint the software cursor directly in SceneQPainter
Summary:
No need to delegate the painting of the software cursor into the backend.
The core has enough information to perform the rendering itself.
This change means less code duplication and all platforms which might use
a software cursor in QPainter compositor gain support for it without any
further adjustments.
Reviewers: KWin, Plasma on Wayland
Subscribers: plasma-devel, kwin
Tags: Plasma on Wayland, KWin
Differential Revision: https://phabricator.kde.org/D2028