chore(query): fix order for scalar cmp with null

[sundy-li]

I hereby agree to the terms of the CLA available at: https://docs.databend.com/dev/policies/cla/

Summary

By default, null is biggest than other values in databend. So we enable Scalar::Null compare with other none null scalars.

• Fixes #[Link the issue here]

Tests

• Unit Test
• Logic Test
• Benchmark Test
• No Test - Explain why

Type of change

• Bug Fix (non-breaking change which fixes an issue)
• New Feature (non-breaking change which adds functionality)
• Breaking Change (fix or feature that could cause existing functionality not to work as expected)
• Documentation Update
• Refactoring
• Performance Improvement
• Other (please describe):

[sundy-li]

Bug in main for merge join, because it did not consider about null

drop table if exists t1;

drop table if exists t2;

create table t1(a int null);

insert into t1 values(1), (NULL), (2);

create table t2(b int null);

insert into t2 values(1), (NULL), (3);

select * from t1 join t2 on t1.a <= t2.b order by t1.a;