Fix TopN distributed plan to wrap partial TopN plan in merge TopN plan

I'm creating a distributed query plan formatter and realized that TopNNode with partial=true wraps TopNNode with partial=false.
For example, with this query: `select r_regionkey from tpch.region order by r_regionkey limit 2`
distributed query plan is:

```
- Stage-1
    -> Output[6]
        Columns: r_regionkey = r:bigint
        -> PartialTopN[9]
            Count: 2
            OrderBy: r ASC NULLS LAST
            -> Exchange[8]
                Sources: Stage-0
- Stage-0
    -> Sink[7]
        -> FinalTopN[2]
            Count: 2
            OrderBy: r ASC NULLS LAST
            -> TableScan[0]
                Table: tpch.region
                Columns: r:bigint = r_regionkey
```

PartialTopN plan node wraps FinalTopN plan, which should be opposite.
I think DistributedLogicalPlanner.visitTopN is creating wrong TopNNode combination.