[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.

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