Make construction previews local entities (fix rP24279)

Identity classes where added to construction previews in D576 / rP24279. This meant they counted towarde entity limits, as they were not local entities.

This diff fixes that by making them local entities.

Thanks for s0600204 for raising the issue

Reported by: wowgetoffyourcellphone

Refs #2907

Differential Revision: https://code.wildfiregames.com/D3187