ARROW-5348: [Java][CI] Add missing gandiva javadoc

[emkornfield]

No description provided.

[praveenbingo]

LGTM.

[codecov-io]

Codecov Report

Merging #4327 into master will increase coverage by 23.7%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master   #4327      +/-   ##
=========================================
+ Coverage   65.49%   89.2%   +23.7%     
=========================================
  Files         527     632     +105     
  Lines       66435   86482   +20047     
  Branches     1251       0    -1251     
=========================================
+ Hits        43513   77144   +33631     
+ Misses      22686    9338   -13348     
+ Partials      236       0     -236

Impacted Files	Coverage Δ
cpp/src/arrow/compute/kernel.h	62.76% <0%> (-3.34%)	⬇️
cpp/src/plasma/thirdparty/ae/ae.c	70.75% <0%> (-0.95%)	⬇️
cpp/src/arrow/csv/column-builder.h	100% <0%> (ø)	⬆️
cpp/src/arrow/table_builder.h	100% <0%> (ø)	⬆️
cpp/src/arrow/compute/kernels/cast.h	100% <0%> (ø)	⬆️
go/arrow/ipc/writer.go
go/arrow/math/uint64_amd64.go
go/arrow/memory/memory_avx2_amd64.go
go/arrow/ipc/file_reader.go
js/src/enum.ts
... and 593 more

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