feat(Core/Grids): Implement visibility notifier (#15919)

* Cherry-picked from TrinityCore (unable to find author)

src/server/game/Grids/Notifiers/GridNotifiersImpl.h

@@ -38,9 +38,6 @@ inline void Acore::VisibleNotifier::Visit(GridRefMgr<T>& m)
 
     for (typename GridRefMgr<T>::iterator iter = m.begin(); iter != m.end(); ++iter)
     {
-        if (i_largeOnly != iter->GetSource()->IsVisibilityOverridden())
-            continue;
-
         vis_guids.erase(iter->GetSource()->GetGUID());
         i_player.UpdateVisibilityOf(iter->GetSource(), i_data, i_visibleNow);
     }