Support multi args for unnest (#909)

Signed-off-by: jayzhan211 <jayzhan211@gmail.com>
Co-authored-by: Andrew Lamb <andrew@nerdnetworks.org>

src/test_utils.rs

@@ -197,6 +197,7 @@ pub fn expr_from_projection(item: &SelectItem) -> &Expr {
     }
 }
 
+/// Creates a `Value::Number`, panic'ing if n is not a number
 pub fn number(n: &'static str) -> Value {
     Value::Number(n.parse().unwrap(), false)
 }