This method needs javadoc to explain what "all" means.

Also, this really should just be for internal use rather on the public `EntityManager` api. It gives access to entities that are not yet managed, which is really an internal-only thing.

Suggest we create an `EntityManagerInternal` with this method, have `LocalEntityManager` implement that, and cast when we need to call this specific method. See `ManagementContextInternal` for an example of that pattern.