[client] Wrap wl_shell_surface_set_{class,title}

Summary: We have to wrap these two requests just for convenience.

Reviewers: #kwin, davidedmundson

Reviewed By: #kwin, davidedmundson

Subscribers: davidedmundson, kde-frameworks-devel

Tags: #frameworks

Differential Revision: https://phabricator.kde.org/D18440