apply constant folding to LogicalPlan::Values

[jimexist]

I suspect it is not likely to matter, but constant folding could be applied to the Exprs in values. As written this code will not apply constant folding to those expressions

Originally posted by @alamb in #1165 (comment)

[viirya]

Hmm, I actually saw LogicalPlan::Values among the logical plans in constant folding optimizer rule now. Is this already resolved?

[viirya]

Ran a test:

    #[test]
    fn optimize_plan_support_values() -> Result<()> {
        let expr1 = Expr::BinaryExpr {
            left: Box::new(lit(1)),
            op: Operator::Plus,
            right: Box::new(lit(2)),
        };
        let expr2 = Expr::BinaryExpr {
            left: Box::new(lit(2)),
            op: Operator::Minus,
            right: Box::new(lit(1)),
        };
        let values = vec![vec![expr1, expr2]];
        let plan = LogicalPlanBuilder::values(values)?.build()?;

        let expected = "\
        Values: (Int32(3), Int32(1))";

        assert_optimized_plan_eq(&plan, expected);
        Ok(())
    }

Looks it already did constant folding?

Maybe we just need to add the test?

[alamb]

Thanks @viirya -- yes I think the general purpose constant folding implementation we have now should handle the Values. Thanks for the test !