Use new toolbox icon for "Tools" dropdown menu button

Summary: Use the awesome new tools icon in the Tools dropdown menu button. Since the icon is only available in Frameworks 5.55, we use the old icon as a fallback since the minimum frameworks version is still 5.29.

Test Plan:

Reviewers: Spectacle, VDG, ndavis

Reviewed By: VDG, ndavis

Subscribers: broulik

Tags: Spectacle

Differential Revision: https://phabricator.kde.org/D18400