Add unary_cmp

[viirya]

Which issue does this PR close?

Closes #1987.

Rationale for this change

What changes are included in this PR?

Are there any user-facing changes?

[codecov-commenter]

Codecov Report

Merging #1991 (1793862) into master (ccddaa8) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1991   +/-   ##
=======================================
  Coverage   83.57%   83.57%           
=======================================
  Files         221      222    +1     
  Lines       57482    57550   +68     
=======================================
+ Hits        48043    48100   +57     
- Misses       9439     9450   +11     

Impacted Files	Coverage Δ
arrow/src/compute/kernels/comparison.rs	92.59% <100.00%> (+0.03%)	⬆️
arrow/src/array/array_map.rs	83.07% <0.00%> (-1.74%)	⬇️
arrow/src/array/array_union.rs	90.14% <0.00%> (-0.78%)	⬇️
...row/src/array/builder/string_dictionary_builder.rs	91.36% <0.00%> (-0.37%)	⬇️
parquet/src/encodings/encoding.rs	93.43% <0.00%> (-0.20%)	⬇️
arrow/src/array/array.rs	92.05% <0.00%> (-0.16%)	⬇️
arrow/src/array/mod.rs	100.00% <0.00%> (ø)
arrow/src/json/reader.rs	84.58% <0.00%> (ø)
arrow/src/array/array_decimal.rs	92.88% <0.00%> (ø)
arrow/src/array/array_primitive.rs	95.81% <0.00%> (+0.03%)	⬆️
... and 11 more

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[viirya]

Unrelated error:

/usr/bin/ld: final link failed: No space left on device

[tustvold]

Perhaps we could inline the macro in unary_op and make the other functions use it 🤔. Less macros is always good imo

[viirya]

Perhaps we could inline the macro in unary_op and make the other functions use it 🤔. Less macros is always good imo

Good idea!

I just tried it. However, compare_op_scalar as a macro is applied on not only PrimitiveArray, but also others like GenericStringArray. But unary_cmp API as a function is bound to PrimitiveArray only.

[alamb]

❤️ thank you @viirya