main: Initialize Wayland just before MetaDisplay

Wayland support is not really a "backend" thing, it just lacked a better
place to store its instance pointer. Eventually we'll have a better
place, but prepare for that by initializing it together with the more
similar subsystems.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1833>

src/backends/native/meta-backend-native.c

@@ -234,10 +234,6 @@ meta_backend_native_post_init (MetaBackend *backend)
 #endif
 
   update_viewports (backend);
-
-#ifdef HAVE_WAYLAND
-  meta_backend_init_wayland (backend);
-#endif
 }
 
 static MetaMonitorManager *

src/backends/x11/nested/meta-backend-x11-nested.c

@@ -243,10 +243,6 @@ meta_backend_x11_nested_post_init (MetaBackend *backend)
     META_BACKEND_CLASS (meta_backend_x11_nested_parent_class);
 
   backend_class->post_init (backend);
-
-#ifdef HAVE_WAYLAND
-  meta_backend_init_wayland (backend);
-#endif
 }
 
 static gboolean