Fix missing entries in context menu for links

Summary: https://cgit.kde.org/dolphin.git/commit/?id=86f4fcb8cd574f6d886627fc5e01c9edfc84e977 introduced a regression: the context menu for links no longer shows various items that were gated behind being a directory. However, a link can be both a link and a directory, from KIO's perspective. This patch resolves the issue.

Test Plan:

• Context menus for files, folders, and file links are unchanged.
• The missing context menu items for folder links have returned:
  

I should have tested that patch better, and for that I apologize and offer to fix this regression here. I will endeavor to up my reviewing game.

Reviewers: rominf, michaelh, Dolphin, rkflx

Reviewed By: rominf, rkflx

Subscribers: rkflx

Differential Revision: https://phabricator.kde.org/D11562