sql: tuple star expansion in tuple context should flatten #28203
Description
Found by @jordanlewis while reviewing #28151 / #28143.
In postgres:
jordan=# SELECT ((i.keys).*, 123) FROM (SELECT information_schema._pg_expandarray(ARRAY[3,2,1]) AS keys) AS i;
row
-----------
(3,1,123)
(2,2,123)
(1,3,123)
In CockroachDB this gets us:
((3,1),123)
((2,2),123)
((1,3),123)
This is incorrect - the tuple should be flattened.
Jira issue: CRDB-4921