PagePainter::paintCroppedPageOnPainter had a few calls to
QPixmap::setDevicePixelRatio on pixmaps it does not own, which detaches
the pixmap, making a deep copy. It turns out these were all unnecessary.
It also copied scaled before drawing them onto the painter.
I've tested all the changes except for the annotation stamps, which I'm
just assuming works like the others.
Also ran clang-format.
QLinkedList is deprecated in later Qt5 and gone in Qt6
The 1:1 port is std::list but in this cases all we ever do
is create the lists, push back to them, and pass then around
to be read, for that a QList is more than enough
