Folderspanel's context-menu option "Limit to Home Directory" is always visible

Summary:
Applied suggested changes to D9662

• Enum instead of bool
• Use QStringLiteral

Test Plan: Visual inspection

Reviewers: ngraham, elvisangelaccio, Dolphin

Reviewed By: ngraham, Dolphin

Subscribers: Dolphin

Tags: Dolphin, KDE Applications

Differential Revision: https://phabricator.kde.org/D9911