Add Send to the ArrayBuilder trait

[Max-Meldrum]

Adds Send to ArrayBuilder.

Closes #290

[codecov-commenter]

Codecov Report

Merging #291 (8e3591c) into master (ce8e67c) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #291   +/-   ##
=======================================
  Coverage   82.49%   82.49%           
=======================================
  Files         162      162           
  Lines       43980    43980           
=======================================
  Hits        36282    36282           
  Misses       7698     7698           

Impacted Files	Coverage Δ
arrow/src/array/builder.rs	85.29% <ø> (ø)
arrow/src/util/display.rs	29.72% <0.00%> (-0.83%)	⬇️
...-testing/src/bin/flight-test-integration-client.rs	0.00% <0.00%> (ø)
...-testing/src/bin/flight-test-integration-server.rs	0.00% <0.00%> (ø)

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[jorgecarleitao]

LGTM. Thanks @Max-Meldrum !

[alamb]

The integration test failure seemed related to some network problem. I have retriggered it