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ARROW-15121: [C++] Implement max recursion on GcsFileSystem

Recursive listing without limit is about as expensive as only listing
the top-level directories in GCS. Therefore, it is just *more* efficient
to filter the results on the client-side, as this requires fewer request
than listing only only 0, 1, or N levels in a directory hierarchy.

I also improved the tests to verify no objects with similar prefixes are
returned, for example, when listing objects starting with 'aaa' we do
not want 'aaab', but we want 'aaa/b'.

Closes #11969 from coryan/ARROW-15121-gcsfs-implement-max-recursion

Authored-by: Carlos O'Ryan <coryan@google.com>
Signed-off-by: Antoine Pitrou <antoine@python.org>