Another unneeded feature related to clutter originally being an application library that we have no use for when we're only ever a compositor. https://gitlab.gnome.org/GNOME/mutter/merge_requests/616
The const qualifiers were implicitly discarded here and there. Avoid that either by adding the constness, or casting it away when a const variable is passed to a function that is defined as non-const but effectively expect a const.
