After fixing pixelated indicator arrows in `KShortcutsEditorDelegate`
(i.e. a subclass, see kxmlgui!104) used in the
"Configure Keyboard Shortcuts" dialog, they were not drawn centered
anymore, e.g. slightly moved upwards. The same problem can be observed
in the download list of KGet.

This is because the increased size of the pixmap is not accounted for.

By transforming the pixmap size to device independent dimensions
again, as used in the positioning calculations, the arrows will finally
be shown correctly.

Note that running `KItemViews` in conjunction with a version of
`KXmlGUI` not including the fix will still work fine, since the
`devicePixelRatio` will only ever be set to `1` in that case.

CCBUG: 414904

Test Plan:
  - Launch `QT_SCALE_FACTOR=1.7 ./bin/kxmlguiwindowtest`
    (from KXmlGui, including the fix mentioned above).
  - Open "Configure Keyboard Shortcuts" dialog.
  - Arrows in "Shortcut" column positioned correctly, for both their
    expanded and collapsed states.
  - Test with `-style Fusion` and other scaling factors, too.
  - `QT_SCALE_FACTOR=1.7 kget`, start download, observe indicator arrow
    in download list.