mutter-clutter is a private library that is only used by the shell and
not meant to be ABI/API compatible in between versions, so there's no
need to add padding to classes.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2903>
Similar to the clutter commits
- Drop all the private structs documentations
- Make use of gi-docgen items linking as much as possible
- Use markdown formatting for code snippets
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2441>