Support Array logical operator to transform subquery results into an array

[maropu]

In PostgreSQL, ARRAY is not a function but a syntax defined in parser definition. So, Spark-2.2 can't handle some queries for metadata handling. See:

spark-sql-server/sql/sql-server/src/test/scala/org/apache/spark/sql/server/PsqlCommandsSuite.scala

Line 260 in ed3e1ed

// In PostgreSQL, `ARRAY` is not a function but a syntax defined in parser definition