Constant group by keys should handle ARRAY[], MAP() etc that are constants

[kaikalur]

SELECT count(1), orderdate, array[] from orders group by 2,3

does still a group by both the keys in the plan. It should hoist that ARRAY[] as well. Basically instead of ConstantExpression, it should use the RowExpressionInterpreter to eval const in the PullConstantsAboveGroupBy optimizer.