Authorization Policy vNext -> Nested Table References

To further enhance the authorization policy capability, add the ability to map to nested tables/columns. For example:

- Database Policy: Entity (book) `"New Starch Press" eq @item().publisher_id.name`

Because the policy is applied to the book entity, the nested policy will search the Publishers table using publisher_id to acquire the record where name column is "New Starch Press"

Nesting will apply to the `@item` "Policy Expression System Object" described in the [request authorization RFC](https://github.com/Azure/project-hawaii/blob/main/rfcs/request-authorization.md#policy-expression-system-objects).

Read the request authorization RFC section on Policy Expression System Objects first, then trace how the current authorization policy evaluates @item references. Define the nested table and column lookup behavior shown in the example, including how the related record is selected and how completion would be verified across the supported API paths.

Written by the indexing model from the issue text.