Comparison Kernels Ignore Nulls in Dictionary Values

[tustvold]

Describe the bug

The dictionary comparison kernels fail to account for nulls nested within dictionaries

To Reproduce

fn test_dictionary_nested_nulls() {
    let keys = Int32Array::from(vec![0, 1, 2]);
    let v1 = Arc::new(Int32Array::from(vec![Some(0), None, Some(2)]));
    let a = DictionaryArray::new(keys.clone(), v1);
    let v2 = Arc::new(Int32Array::from(vec![None, Some(0), Some(2)]));
    let b = DictionaryArray::new(keys, v2);

    let r = eq_dyn(&a, &b).unwrap();
    assert_eq!(r.null_count(), 2);
}

Expected behavior

Additional context

[tustvold]

label_issue.py automatically added labels {'parquet'} from #4691

[tustvold]

label_issue.py automatically added labels {'arrow'} from #4691