The intention was to add a license header the same as other files in the mutter backend files, so make it so. Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1690>
The pixel format helper will be reused by the next commits, and it doesn't make sense to simply expose it as MetaRendererNative API. Move it to a separate file. https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1421