RelToSqlConverter[ORDER BY] generates an incorrect order by when NULLS LAST is used in non-projected field

We are using RelToSqlConverter, and seeing issues with it generating invalid queries when using DESC NULLS LAST, specifically.

For example, this test query:

select "product_id"
from "product"
where "net_weight" is not null
group by "product_id"
order by MAX("net_weight") desc 

Gets resolved correctly, with a subquery, to:

SELECT "product_id"
FROM (SELECT "product_id", MAX("net_weight") AS "EXPR$1"
FROM "foodmart"."product"
WHERE "net_weight" IS NOT NULL
GROUP BY "product_id"
ORDER BY 2 DESC) AS "t3" 

However, if I specify `desc nulls last`:

select "product_id"
from "product"
where "net_weight" is not null
group by "product_id"
order by MAX("net_weight") desc nulls last 

It creates an invalid query (order by 2, but only one field was projected):

SELECT "product_id"
FROM "foodmart"."product"
WHERE "net_weight" IS NOT NULL
GROUP BY "product_id"
ORDER BY 2 DESC NULLS LAST 

Trying to troubleshoot it, it appears that without the `NULLS LAST`, we have the following instance:

SqlBasicCall -> SqlNumericLiteral 

But when including it, it gets wrapped in another call:

SqlBasicCall -> SqlBasicCall -> SqlNumericLiteral 

So the hasSortByOrdinal method ends up returning false, which causes `needNewSubQuery` to incorrectly report false too.

It appears that the best way to deal with this is by using a recursion to find numeric literals - but let me know if there are better ideas. 

I plan to take a stab at this since I got enough context.