Fix linked objects not appearing after dragging in from Asset Browser

When the Asset Browser import type was set to "Link", after dragging in an
object asset the object wouldn't actually appear in the viewport. Do the same
depsgraph tagging (and TODO comment) as the `OBJECT_OT_add_named` operator,
which does similar things.

source/blender/editors/space_view3d/space_view3d.c

@@ -85,6 +85,7 @@
 #endif
 
 #include "DEG_depsgraph.h"
+#include "DEG_depsgraph_build.h"
 
 #include "view3d_intern.h" /* own include */
 
@@ -747,6 +748,8 @@ static void view3d_ob_drop_copy_external_asset(wmDrag *drag, wmDropBox *drop)
 
   ID *id = WM_drag_asset_id_import(asset_drag, FILE_AUTOSELECT);
 
+  /* TODO(sergey): Only update relations for the current scene. */
+  DEG_relations_tag_update(CTX_data_main(C));
   WM_event_add_notifier(C, NC_SCENE | ND_LAYER_CONTENT, scene);
 
   RNA_string_set(drop->ptr, "name", id->name + 2);