ARROW-11442: [Rust] Expose datetime conversion logic independently

[jorgecarleitao]

This is a small refactor that exposes the functions used to convert dates and times into NaiveDate, NaiveTime and NaiveDateTime. They are currently hidden beind the PrimitiveArray<ArrowTemporalType>::value_as_time, which makes them difficult to use when the transformation is to be applied in SIMD, or when we want to reproduce the operation for a single scalar value (not in an arrow array).

[github-actions]

https://issues.apache.org/jira/browse/ARROW-11442

[codecov-io]

Codecov Report

Merging #9378 (6310c6d) into master (f05b49b) will increase coverage by 0.01%.
The diff coverage is 97.50%.

@@            Coverage Diff             @@
##           master    #9378      +/-   ##
==========================================
+ Coverage   81.94%   81.96%   +0.01%     
==========================================
  Files         231      231              
  Lines       53374    53372       -2     
==========================================
+ Hits        43739    43748       +9     
+ Misses       9635     9624      -11     

Impacted Files	Coverage Δ
rust/arrow/src/array/array_primitive.rs	94.74% <91.66%> (-0.21%)	⬇️
rust/arrow/src/temporal_conversions.rs	100.00% <100.00%> (ø)
rust/parquet/src/encodings/encoding.rs	94.86% <0.00%> (-0.20%)	⬇️
rust/datafusion/src/physical_plan/hash_join.rs	83.52% <0.00%> (-0.15%)	⬇️
rust/datafusion/src/logical_plan/builder.rs	88.20% <0.00%> (-0.07%)	⬇️
rust/datafusion/src/optimizer/optimizer.rs
rust/datafusion/src/sql/planner.rs	84.17% <0.00%> (+0.01%)	⬆️
rust/datafusion/src/physical_plan/planner.rs	78.78% <0.00%> (+0.14%)	⬆️
rust/datafusion/src/execution/context.rs	89.21% <0.00%> (+0.49%)	⬆️
... and 2 more

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[Dandandan]

This looks good 👍! This would also be helpful for removing some indirection in the temporal kernels. Maybe the module name could be called temporal_conversions or datetime_conversions?

[alamb]

Looks good to me. Thanks @jorgecarleitao

[alamb]

I think this is small enough / not backwards breaking to merge. So doing so