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ARROW-8506: [C++] Add tests to verify the encoded stream of RLE with bit_width > 8

This PR adds test cases to verify whether the encoded values are stored in a little-endian format when RLE with bit_width > 8 is applied. Parquet encoder/decoder handles the value as little-endian as follows:
https://github.com/apache/parquet-mr/blob/master/parquet-column/src/main/java/org/apache/parquet/column/values/rle/RunLengthBitPackingHybridEncoder.java#L244
https://github.com/apache/parquet-mr/blob/master/parquet-column/src/main/java/org/apache/parquet/column/values/rle/RunLengthBitPackingHybridDecoder.java#L87

There is no test of this type in the current test cases of Rle.

Closes #6976 from kiszk/ARROW-8506

Authored-by: Kazuaki Ishizaki <ishizaki@jp.ibm.com>
Signed-off-by: Antoine Pitrou <antoine@python.org>