Serialize i128 as JSON string

[tustvold]

Which issue does this PR close?

Closes #1174

Rationale for this change

See ticket

What changes are included in this PR?

This changes i128 to be JSON serialized as a string

Are there any user-facing changes?

I think so, I'm not very familiar with arrow's JSON interface nor what it is used for

[houqp]

LGTM, thanks @tustvold . I think there are couple other unit tests that need to be updated.

[tustvold]

The failures seem unrelated to my change, and I'm struggling to reproduce them locally...

Edit: Huzzah, updating to rust toolchain 1.58 can reproduce 🤔

[codecov-commenter]

Codecov Report

Merging #1175 (f58c4c0) into master (66b84f3) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1175   +/-   ##
=======================================
  Coverage   82.66%   82.66%           
=======================================
  Files         173      173           
  Lines       50902    50902           
=======================================
+ Hits        42077    42078    +1     
+ Misses       8825     8824    -1     

Impacted Files	Coverage Δ
arrow/src/datatypes/mod.rs	100.00% <100.00%> (ø)
arrow/src/datatypes/native.rs	66.66% <100.00%> (ø)
arrow/src/datatypes/datatype.rs	66.38% <0.00%> (-0.43%)	⬇️
arrow/src/array/transform/mod.rs	85.43% <0.00%> (-0.14%)	⬇️
parquet/src/encodings/encoding.rs	93.71% <0.00%> (+0.19%)	⬆️
parquet_derive/src/parquet_field.rs	66.43% <0.00%> (+0.45%)	⬆️

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[alamb]

Thanks @tustvold