x11-display: Get _NET_WM_NAME from context

It's equivalent to the name that was passed when the context was
created.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1861>

src/core/meta-context-private.h

@@ -45,6 +45,8 @@ struct _MetaContextClass
   void (* notify_ready) (MetaContext *context);
 };
 
+const char * meta_context_get_name (MetaContext *context);
+
 MetaWaylandCompositor * meta_context_get_wayland_compositor (MetaContext *context);
 
 #endif /* META_CONTEXT_PRIVATE_H */