Support Array constructor

[big-andy-coates]

We do not currently have support for creating instances of ARRAYs. Our SQL grammar does have rules for this: ARRAY[1,2,3] should create an array.

We should support arrays being created with literals, e.g. ARRAY[1,2,3] and with expressions, e.g. ARRAY[col1, 1 + 2, col3 / col4, max(col5, col6)].

We should support constructed arrays being used in:

• INSERT VALUES statements - it's currently not possible to insert an array into an existing source.
• SELECT expressions, e.g. SELECT ARRAY[col0, col1] FROM ...
• WHERE/HAVING expressions, e.g. WHERE col0 = ARRAY[0,2]
• GROUP BY, e.g. GROUP BY ARRAY[col0, col1]
• etc

[agavra]

As a workaround (does not work in INSERT VALUES) I introduced the AS_ARRAY UDF. I think a valuable improvement would be to also allow INSERT VALUES to use UDFs.