Implement DecimalArray support in eq_dyn, neq_dyn, lt_dyn, lt_eq_dyn, gt_dyn, gt_eq_dyn

[alamb]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
Rationale make it as easier (more ergonomic) to implement array comparison, both for DataFusion and other users. See rationale in #843

Describe the solution you'd like
The idea would basically be to implement the same thing as @viirya did for timestamp types in #1095 but for DecimalArrays

That is the following code should not assert and compare the decimal arrays element by element:

let arr1: DecimalArray = ...;
let arr2: DecimalArray = ...;
let result = eq_dyn(&arr1, &arr2);
assert!(result.is_ok())

Describe alternatives you've considered
For completeness, we could also add eq_decimal, neq_decimal, etc as well, though I personally think focusing on the dyn kernels would be the easiest thing.

Additional context

@liukun4515 has added kernels in DataFusion here which could be adapted
https://github.com/apache/arrow-datafusion/blob/master/datafusion/src/physical_plan/expressions/binary.rs#L80-L231

other context:
I am trying to move datafusion over to using the dyn kernels here: apache/datafusion#1475

[liukun4515]

@alamb Do you begin to do this?
If not, I can try it.

[alamb]

@liukun4515 I have not started this

[viirya]

Any more progress? If no, I may find some time working on this.

[alamb]

I have not made any progress on this sadly

[liukun4515]

Any more progress? If no, I may find some time working on this.

I will do this when the kernel functions are ready in the datafusion side.
@viirya

[alamb]

I think the idea is to

1. port / move the eq_decimal from datafusion to arrow-rs
2. hook up the kernels to the dispatch in eq_dyn, etc

Here is the code in datafusion
https://github.com/apache/arrow-datafusion/blob/7b7edf9c43383c1d3310286b69d2d037db72c967/datafusion/physical-expr/src/expressions/binary.rs#L169

Needs to brought to https://sourcegraph.com/github.com/apache/arrow-rs/-/blob/arrow/src/compute/kernels/comparison.rs?L7&subtree=true

and then also added to eq_dyn https://sourcegraph.com/github.com/apache/arrow-rs/-/blob/arrow/src/compute/kernels/comparison.rs?L2324:8-2324:14

[liukun4515]

I think it has been done.
cc @alamb @tustvold

[liukun4515]

we can close it.