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PARQUET-2008: [C++] Fix information written in RowGroup::total_byte_size

We need to write out the uncompressed size (including headers), not the compressed size.

This matches parquet-mr's behaviour.

Closes #9791 from pitrou/PARQUET-2008-total-byte-size

Authored-by: Antoine Pitrou <antoine@python.org>
Signed-off-by: Antoine Pitrou <antoine@python.org>