Move simd right out of for_each loop

[viirya]

Which issue does this PR close?

Closes #.

Rationale for this change

For the scalar part of simd array and scalar operation, we don't need to initiate a vector for the scalar every time.

What changes are included in this PR?

Move scalar part out of for_each loop in simd operation between array and scalar.

Are there any user-facing changes?

No

[codecov-commenter]

Codecov Report

Merging #1150 (fc1e998) into master (719096b) will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1150   +/-   ##
=======================================
  Coverage   82.55%   82.56%           
=======================================
  Files         169      169           
  Lines       50456    50497   +41     
=======================================
+ Hits        41655    41691   +36     
- Misses       8801     8806    +5     

Impacted Files	Coverage Δ
arrow/src/compute/kernels/arithmetic.rs	84.14% <ø> (ø)
arrow/src/datatypes/datatype.rs	66.38% <0.00%> (-0.43%)	⬇️
arrow/src/datatypes/field.rs	53.79% <0.00%> (-0.31%)	⬇️
arrow/src/array/transform/mod.rs	85.43% <0.00%> (-0.27%)	⬇️
parquet_derive/src/parquet_field.rs	66.21% <0.00%> (-0.23%)	⬇️
parquet/src/compression.rs	88.59% <0.00%> (ø)
parquet/src/arrow/arrow_writer.rs	98.07% <0.00%> (ø)
arrow/src/compute/kernels/comparison.rs	91.96% <0.00%> (ø)
arrow/src/array/array_string.rs	97.40% <0.00%> (+0.32%)	⬆️
arrow/src/util/test_util.rs	92.04% <0.00%> (+1.13%)	⬆️

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[jhorstmann]

Probably doesn't change the performance since the compiler would do this automatically, but makes the inner loop a bit easier to read 👍

[alamb]

Thank you for the contribution @viirya and the reviews @jhorstmann and @houqp ❤️

[viirya]

Thank you @houqp @jhorstmann @alamb