[VL] Fix native union use column type name as column name lead to result error

[lifulong]

What changes are proposed in this pull request?

Fix native union result use column type name as column name, which lead to same data type column has same data, but is not right result. eg all string columns has same data value as the first string column

const auto name = outRowType->childAt(colIdx)->name();
result name is column type name
const auto name = outRowType->nameOf(colIdx);
result name is column name

with conf spark.gluten.sql.native.union=true and use sql like

with deduplicated_data as (
  select col1, col2, col3, col4, col6
  from (
    select
      u.col1,
      u.col2,
      u.col3,
      u.col4,
      u.col6,
      row_number() over (partition by u.col2 order by u.col5 desc) as rn
    from (
      select col1, col2, col3, col4, 98 as col5, '' as col6 from union_src_a
      union all
      select col1, col2, col3, col4, 100 as col5, '' as col6 from union_src_b
    ) u
  ) t
  where t.rn = 1
)
select col1, col2, col3, col4
from deduplicated_data
where col1 != 'valueC'
union all
select col1, col2, col3, col4
from deduplicated_data
where col1 = 'valueC'
``` can reproduce the error

## How was this patch tested?

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test at our produce env, and add unit test
## Was this patch authored or co-authored using generative AI tooling?
yes, co-authored by cursor
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[lifulong]

the error is clear, reproduce error result need complex union sql, maybe no need add unittest, i am not sure