SQL/JSON: Fix JSON_QUERY(... WITH CONDITIONAL WRAPPER)

SQL/JSON: Fix JSON_QUERY(... WITH CONDITIONAL WRAPPER)

Currently, when WITH CONDITIONAL WRAPPER is specified, array wrappers
are applied even to a single SQL/JSON item if it is a scalar JSON
value, but this behavior does not comply with the standard.

To fix, apply wrappers only when there are multiple SQL/JSON items
in the result.

Reported-by: Peter Eisentraut <[email protected]>
Author: Peter Eisentraut <[email protected]>
Author: Amit Langote <[email protected]>
Reviewed-by: Andrew Dunstan <[email protected]>
Discussion: https://postgr.es/m/8022e067-818b-45d3-8fab-6e0d94d03626%40eisentraut.org
Back-through: 17