[Folder View] Improve file name text rendering

GridView pads out its delegate to ensure a uniform grid. This, however, causes items to be placed on fractional pixels,
leading to blurry rendering and uneven hinting.
Instead of adjusting padding calculation to return whole pixels, which will again cause a gap at the right side of the screen,
since there's 20 icons in a row, slightly shift the delegate contents to move them back to whole pixels.
Moreover, DropShadow renders the entire item with a drop shadow, so keeping the Label visible results in two labels ontop of
each other leading to bolder text.

Differential Revision: https://phabricator.kde.org/D14234