add DuckDB variant result

[qsliu2017]

DuckDB v1.5.0 introduces variant type. IMO, this is an alternative binary JSON. will you accept result replacing JSON with variant?

[rschu1ze]

Generally yes.

I am not really familiar with DuckDB's type system. Is VARIANT supposed to be the successor of JSON? I wonder why in the corresponding PR it says that roundtrip conversions between JSON and VARIANT are lossy and thus excluded?