[Rotate Dialog] Use themed rotate (anti)clockwise icons

Got bothered by the blocky look on highdpi, looks a lot nicer :)

Somehow the Adwaita theme here doesn't load properly.

object-rotate-left and object-rotate-right are part of the FDO icon name spec [1].

Before

After (Breeze)

After (Oxygen)

The check for whether we got a fallback to object-rotate or object (which we don't want here) does not work due to a bug in KIconEngine, cf. https://bugs.kde.org/show_bug.cgi?id=432293 – QIcon::name() always returns whatever you passed in even if the icon you got didn't actually go by that name.

@dfaure @heikobecker @mkoller @teams/vdg

[1] https://specifications.freedesktop.org/icon-naming-spec/icon-naming-spec-latest.html#:~:text=an%20object%20vertically.-,object-rotate-left,-The%20icon%20for