ARROW-5821: [Java] Support compact fixed-width vectors

[tianchen92]

Related to ARROW-5821.
In shuffle stage of some applications, FixedWitdhVectors may have very little non-null data.
In this case, directly serialize vectors is not a good choice, generally we can compact the vector make it only holding non-null value and create a BitVector to trace the indices for non-null values so that it could be deserialized properly.

[codecov-io]

Codecov Report

Merging #4789 into master will increase coverage by 17.33%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #4789       +/-   ##
==========================================
+ Coverage   72.26%   89.6%   +17.33%     
==========================================
  Files         822     662      -160     
  Lines      107713   96352    -11361     
  Branches     1418       0     -1418     
==========================================
+ Hits        77844   86332     +8488     
+ Misses      29507   10020    -19487     
+ Partials      362       0      -362

Impacted Files	Coverage Δ
cpp/src/arrow/testing/gtest_util.h	97.36% <0%> (-2.64%)	⬇️
cpp/src/arrow/compute/kernel.h	61.16% <0%> (-1.53%)	⬇️
cpp/src/arrow/result.h	91.3% <0%> (-0.37%)	⬇️
cpp/src/arrow/flight/server.h	100% <0%> (ø)	⬆️
cpp/src/gandiva/expression_registry.h	100% <0%> (ø)	⬆️
cpp/src/arrow/csv/column-builder.h	100% <0%> (ø)	⬆️
cpp/src/arrow/table_builder.h	100% <0%> (ø)	⬆️
cpp/src/plasma/plasma.h	100% <0%> (ø)	⬆️
cpp/src/gandiva/configuration.h	100% <0%> (ø)	⬆️
cpp/src/arrow/compute/kernels/cast.h	100% <0%> (ø)	⬆️
... and 746 more

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[emkornfield]

We should maybe close this until we decide if this should be support as part of the encoding/compression discussions?

[tianchen92]

We should maybe close this until we decide if this should be support as part of the encoding/compression discussions?

Sure, closed.