Support typeless STRUCT syntax with field name

[apstndb]

https://cloud.google.com/spanner/docs/reference/standard-sql/data-types#typeless_struct_syntax

Typeless struct syntax

STRUCT( expr1 [AS field_name] [, ... ])

$ go run ./tools/parse --mode query 'SELECT TO_JSON(STRUCT(1 AS a, 'abc' AS b))' 
2024/10/19 17:34:25 syntax error: :1:25: expected token: ), but: AS

  1:  SELECT TO_JSON(STRUCT(1 AS a, abc AS b))
                              ^~
exit status 1

Related discussions

• It should be implemented by separating StructLiteral to TypedStructLiteral and TypelessStructLiteral: Refactor SQL() methods #173 (comment)

[apstndb]

Already resolved via #183