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GH-37002: [C++][Parquet] Add api to get RecordReader from RowGroupReader (#37003)

Currently we only can get a ColumnReader for a column from RowGroupReader. We need an API to return a RecordReader for the column.

Moved ComputeLevelInfo from column_writer to level_conversion so that it can be shared between column_writer and file_reader.
* Closes: #37002

Lead-authored-by: Fatemah Panahi <panahi@google.com>
Co-authored-by: Fatemah Panahi <fatemehp@users.noreply.github.com>
Signed-off-by: Gang Wu <ustcwg@gmail.com>