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PARQUET-2067: [C++][Parquet] Fix Parquet null count stats for enclosing null lists

For repeated columns, the null count should include cases where the
enclosing list(s) is null of empty. For example `[[0, 1], None, [2,
None, 3]]` should have a null count of 2.

Co-authored-by: Micah Kornfield <micahk@google.com>

Closes #11281 from tachyonwill/null_statistics

Authored-by: William Butler <wab@google.com>
Signed-off-by: Antoine Pitrou <antoine@python.org>