Set preview to correct device size
Summary:
QQuickImage::sourceSize is in device pixels for pixmap images.
Converting is the responsibility of the calling code.
BUG: 407689
Test Plan:
QT_SCALE_FACTOR=1.5 kcmshell5 sddm
Looked at image
Reviewers: Plasma, apol
Reviewed By: apol
Subscribers: ngraham, plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D24591