Outliner: Set View Layer as the default mode for new outliners

This mode was supposed to be the new default since 2 years already.

But apparently, it was tackled only for doversion, but not for new
outliners (see 7f596d39df).

source/blender/editors/space_outliner/space_outliner.c

@@ -303,6 +303,7 @@ static SpaceLink *outliner_new(const ScrArea *UNUSED(area), const Scene *UNUSED(
   soutliner->spacetype = SPACE_OUTLINER;
   soutliner->filter_id_type = ID_GR;
   soutliner->show_restrict_flags = SO_RESTRICT_ENABLE | SO_RESTRICT_HIDE;
+  soutliner->outlinevis = SO_VIEW_LAYER;
 
   /* header */
   ar = MEM_callocN(sizeof(ARegion), "header for outliner");