Add an Activities list into the context menu
Summary:
This makes the task manager's context menu match KWin's titlebar context
menu.
BUG: 261649
CCBUG: 360293
Reviewers: Plasma, hein
Reviewed By: Plasma, hein
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D1815