Add "Open symlink destination folder" into symlink's context menu

Summary:
This is not complete. I'm wondering about "Open symlink destination folder in new tab/window".

Feature wants also "Copy symlink destination". I dislike this, because then it's good to have "Cut symlink destination" and that's too much.

FEATURE: 215069

Reviewers: #dolphin, ngraham

Reviewed By: #dolphin, ngraham

Subscribers: rkflx, ngraham, elvisangelaccio, markg, #dolphin

Differential Revision: https://phabricator.kde.org/D10990