ARROW-6300: [C++] Add Abort() method to streams

[pitrou]

This is a quick-close method that does not guarantee it will flush any pending data,
just deallocate ressources held up by the stream.

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@26f631f). Click here to learn what that means.
The diff coverage is 63.02%.

@@            Coverage Diff            @@
##             master    #5274   +/-   ##
=========================================
  Coverage          ?   89.18%           
=========================================
  Files             ?      750           
  Lines             ?   108228           
  Branches          ?        0           
=========================================
  Hits              ?    96528           
  Misses            ?    11700           
  Partials          ?        0

Impacted Files	Coverage Δ
cpp/src/arrow/io/memory.h	100% <ø> (ø)
cpp/src/arrow/io/interfaces.h	90% <ø> (ø)
cpp/src/arrow/io/compressed.h	100% <ø> (ø)
cpp/src/arrow/python/io.h	100% <ø> (ø)
cpp/src/arrow/filesystem/s3_internal.h	100% <ø> (ø)
python/pyarrow/io.pxi	72.18% <ø> (ø)
cpp/src/arrow/filesystem/mockfs.cc	94.64% <0%> (ø)
cpp/src/arrow/io/file.cc	97.66% <100%> (ø)
cpp/src/arrow/io/memory.cc	90.47% <100%> (ø)
cpp/src/arrow/filesystem/s3fs_test.cc	99.23% <100%> (ø)
... and 6 more

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