ARROW-5594: [C++] add UnionArrays support to Take/Filter kernels

[bkietz]

Take and Filter kernels should now be able to operate on arrays of any type.

[pitrou]

Thank you @bkietz ! Looks good on the principle, just a couple comments and questions.

[pitrou]

+1. Will merge if green.

[codecov-io]

Codecov Report

Merging #4866 into master will increase coverage by 1.64%.
The diff coverage is 98.15%.

@@            Coverage Diff             @@
##           master    #4866      +/-   ##
==========================================
+ Coverage   87.46%    89.1%   +1.64%     
==========================================
  Files         994      717     -277     
  Lines      140389   100548   -39841     
  Branches     1418        0    -1418     
==========================================
- Hits       122788    89591   -33197     
+ Misses      17239    10957    -6282     
+ Partials      362        0     -362

Impacted Files	Coverage Δ
cpp/src/arrow/compute/kernels/take.cc	97.29% <100%> (-0.62%)	⬇️
cpp/src/arrow/ipc/json-simple-test.cc	100% <100%> (ø)	⬆️
cpp/src/arrow/compute/kernels/take-test.cc	100% <100%> (ø)	⬆️
cpp/src/arrow/compute/kernels/filter.cc	98.03% <100%> (ø)	⬆️
cpp/src/arrow/compute/kernels/filter-test.cc	100% <100%> (ø)	⬆️
cpp/src/arrow/ipc/json-simple.cc	98.38% <100%> (ø)	⬆️
cpp/src/arrow/compute/kernels/take-internal.h	94.67% <97.45%> (+2.77%)	⬆️
cpp/src/arrow/json/converter.cc	90.53% <0%> (-1.78%)	⬇️
cpp/src/arrow/json/chunked-builder.cc	79.91% <0%> (-1.68%)	⬇️
cpp/src/arrow/csv/parser-test.cc	98.61% <0%> (-1.39%)	⬇️
... and 295 more

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