It was implemented together with MetaStageImpl, move it to a separate file. Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1862>
Rename to MetaStageImpl and MetaStageView, so they are in line with the rest of the backend code. Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1862>
This is now MetaStageImpl in backend code. Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1862>