[RenameDialog] Add an arrow indicating direction from src to dest

Summary:
This adds a visual indication to show the direction of the copy/move..etc
operation pointing from source to destination.

See the screenshots.
{F8274196}
{F8274191}

BUG: 268600

Reviewers: #frameworks, dfaure, meven, ngraham, #dolphin

Reviewed By: meven, ngraham, #dolphin

Subscribers: kde-frameworks-devel

Tags: #frameworks

Differential Revision: https://phabricator.kde.org/D29254