This is a simple clipboard manager implementation on top of MetaSelection.
It will inspect the clipboard content for UTF-8 text and image data whenever
any other selection source claims ownership, and claim it for itself
whenever the clipboard goes unowned.
The stored text has a maximum size of 4MB and images 200MB, to prevent the
compositor from allocating indefinite amounts of memory.
This is not quite a X11 clipboard manager, but also works there.
https://gitlab.gnome.org/GNOME/mutter/merge_requests/320
