When accidentally running a test doing screen-grabbing
with High DPI scaling active, sizes of the obtained pixmaps
can differ due to the device pixel ratio. Add a check to make that
clearer.
[ChangeLog][QtTestLib] Comparison of QImage, QPixmap now checks for the
device pixel ratio.
Change-Id: Id8d5187e99c565c44a7bfb8b9cfb09737815fb15
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>