Add support for wl_shell_surface::set_popup and popup_done
Summary:
This extends the client side API to support creating popup ShellSurface
windows and the server side API to send out the popup_done request.
This is needed to properly support popup windows (e.g. context menus)
in KWin.
Reviewers: Plasma on Wayland, Frameworks, KWin
Subscribers: plasma-devel
Tags: Plasma on Wayland, Frameworks
Differential Revision: https://phabricator.kde.org/D5174