Support dyn_compare_scalar for Decimal256

[izveigor]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
Like Decimal128Array, I think Decimal256Array should be also compared with a scalar.

use arrow::array::{Decimal128Array, Decimal256Array};
use arrow::compute::kernels::comparison::eq_dyn_scalar;
use arrow::datatypes::i256;


fn main() {
    let decimal128_array = Decimal128Array::from(vec![1_i128, 2_i128, 3_i128]);
    let decimal256_array = Decimal256Array::from(vec![i256::from_i128(1), i256::from_i128(2), i256::from_i128(3)]);
    println!("{:#?}", eq_dyn_scalar(&decimal128_array, 2_i64)); // Ok
    println!("{:#?}", eq_dyn_scalar(&decimal256_array, 2_i64)); // Error
}

output:

Ok(
    BooleanArray
    [
      false,
      true,
      false,
    ],
)
Err(
    ComputeError(
        "Unsupported data type Decimal256(76, 10) for comparison eq_scalar with 2",
    ),
)

Should be:
output:

Ok(
    BooleanArray
    [
      false,
      true,
      false,
    ],
)
Ok(
    BooleanArray
    [
      false,
      true,
      false,
    ],
)

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Describe alternatives you've considered

Additional context

[tustvold]

label_issue.py automatically added labels {'arrow'} from #4084