Summary:
We pass the buffer scale of the cursor through QImage::devicePixelRatio.
When copying the cursor with QPainter use Qt's in-built functionality to
handle resizing the cursor pixmap as necessary to match the screen.
As we're now resizing the cursor, the hotspot needs translating from
logical to device co-ordinates.
Test Plan: Used with associated patches
Reviewers: #kwin, graesslin
Reviewed By: #kwin, graesslin
Subscribers: graesslin, kwin
Tags: #kwin
Differential Revision: https://phabricator.kde.org/D13605