ARROW-14559: [C++] reduce memory usage in GcsFileSystem::OpenInputStream
ARROW-14559: [C++] reduce memory usage in GcsFileSystem::OpenInputStream

Closes #11595 from coryan/ARROW-14559-reduce-memory-usage-in-GcsFileSystem-OpenInputStream

Authored-by: Carlos O'Ryan <9e621187562cef94ec9617928f4eb1eb11d57112@google.com>
Signed-off-by: Antoine Pitrou <9359a4d812173b65a3a0094cd86363e79731a3c2@python.org>

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