Remove StringOffsetTrait and BinaryOffsetTrait

[HaoYang670]

Which issue does this PR close?

Closes #1644.

Rationale for this change

What changes are included in this PR?

1. Remove StringOffsetTrait and BinaryOffsetTrait
2. Add get_data_type function for StringArray and BinaryArray (unfortunately, this function cannot be const because OffsetSizeTrait::is_large is not const)

Are there any user-facing changes?

Yes. Delete 2 public traits.

[codecov-commenter]

Codecov Report

Merging #1645 (1b5d943) into master (22e9f95) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1645   +/-   ##
=======================================
  Coverage   83.02%   83.03%           
=======================================
  Files         193      193           
  Lines       55612    55622   +10     
=======================================
+ Hits        46174    46184   +10     
  Misses       9438     9438           

Impacted Files	Coverage Δ
arrow/src/array/builder.rs	86.79% <ø> (ø)
arrow/src/array/equal_json.rs	89.70% <ø> (ø)
arrow/src/array/iterator.rs	96.11% <ø> (ø)
arrow/src/array/mod.rs	100.00% <ø> (ø)
arrow/src/array/ord.rs	69.17% <ø> (ø)
arrow/src/compute/kernels/filter.rs	88.33% <ø> (ø)
arrow/src/compute/kernels/length.rs	100.00% <ø> (ø)
arrow/src/compute/kernels/take.rs	95.41% <ø> (ø)
arrow/src/array/array_binary.rs	93.02% <100.00%> (+0.03%)	⬆️
arrow/src/array/array_string.rs	97.73% <100.00%> (+0.03%)	⬆️
... and 14 more

---

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[viirya]

Hmm, why don't we just make a const is_large in OffsetSizeTrait simply?

pub trait OffsetSizeTrait {
  const IS_LARGE: bool;
}
impl OffsetSizeTrait for i32 {
    const IS_LARGE: bool = false;
}

impl OffsetSizeTrait for i64 {
    const IS_LARGE: bool = true
}

[viirya]

Looks good to me. Just one question above.

[HaoYang670]

Hmm, why don't we just make a const is_large in OffsetSizeTrait simply?

Strongly agree with you!
I will create a follow-up issue to track this.
Tracked in #1658

[tustvold]

Minor nit you can take or leave, will merge later today.

Thanks 👍

[tustvold]

Going to get this in as the merge conflict potential is high

[alamb]

arrow 14 is shaping up for another great release 🎉