refactor regexp_is_match_utf8_scalar to try to mitigate miri failures

[jimexist]

Which issue does this PR close?

Closes #879

Rationale for this change

refactor regexp_is_match_utf8_scalar to try to mitigate miri failures

What changes are included in this PR?

refactor regexp_is_match_utf8_scalar to try to mitigate miri failures

Are there any user-facing changes?

[codecov-commenter]

Codecov Report

Merging #895 (b1a10e0) into master (06f730e) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #895      +/-   ##
==========================================
- Coverage   82.30%   82.30%   -0.01%     
==========================================
  Files         168      168              
  Lines       48031    48031              
==========================================
- Hits        39533    39532       -1     
- Misses       8498     8499       +1     

Impacted Files	Coverage Δ
arrow/src/compute/kernels/comparison.rs	92.63% <100.00%> (ø)
arrow/src/datatypes/datatype.rs	64.93% <0.00%> (-0.44%)	⬇️
parquet_derive/src/parquet_field.rs	66.21% <0.00%> (-0.23%)	⬇️
arrow/src/array/transform/mod.rs	85.33% <0.00%> (+0.13%)	⬆️

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[jimexist]

not sure if moving this out would help but let me try this anyway

[alamb]

This seems like a reasonable code change to me, though I don't think MIRI is failing anymore on master, is it?

https://github.com/apache/arrow-rs/runs/4064195444?check_suite_focus=true

[jimexist]

This seems like a reasonable code change to me, though I don't think MIRI is failing anymore on master, is it?

https://github.com/apache/arrow-rs/runs/4064195444?check_suite_focus=true

I did a retry so not sure why it was fixed I guess I'll merge this as is and see if it resurfaces