[Variant] Improve the get type logic for DataType in variant to arrow row builder

[klion26]

Missing the boolean case?

But actually, I suspect we can get just rid of get_type_name, relying on T::DATA_TYPE and the shiny new impl Display for DataType instead?

(that cleanup would probably be a separate PR tho)

Originally posted by @scovich in #8516

[liamzwbao]

take