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