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ARROW-8756: [C++] Fix Bitmap Words tests' failures on big-endian platforms

This PR adds support of multiple-word operation on big-endian platforms. There are optimized code to concat multiple words into one word with bit shift operations. The current code assumes a little-endian platform.
This code support bit-endian by adding conversions between little-endian and big-endian. This is because the shift operations assume the little-endian layout. It is easy to implement by adding conversions.

With #7136 and this PR, the following failures in arrow-utility-test will be fixed.
```
[  FAILED  ] Bitmap.VisitWordsAnd
[  FAILED  ] Bitmap.ShiftingWordsOptimization
```

Closes #7145 from kiszk/ARROW-8756

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