Summary:
This patch makes use of wlroot's DataControl interface to support
clipboard management.
Unlike wl_data_device clipboards are sent on every change to all
watchers.
If the data device has a selection set it updates immediately.
Because it was started a year ago it uses the existing style of
wrapping objects. The unit test uses the new approach.
Test Plan:
Updated kwin
used wlroot's wl-copy, wl-paste which are xclip replacements to
show that the clipboard updated correctly
Reviewers: #kwin
Differential Revision: https://phabricator.kde.org/D29330
