renderer-view: Keep track of what CRTC it is associated with

For the nested and native backend, it'll point to the CRTC it was
created for. On the X11 CM backend, it'll be NULL, as there is only a
single global stage view.

https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1285

src/backends/meta-renderer-view.h

@@ -28,4 +28,6 @@ G_DECLARE_FINAL_TYPE (MetaRendererView, meta_renderer_view,
 
 MetaMonitorTransform meta_renderer_view_get_transform (MetaRendererView *view);
 
+MetaCrtc *meta_renderer_view_get_crtc (MetaRendererView *view);
+
 #endif /* META_RENDERER_VIEW_H */