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GH-35757: [C++][Parquet] using page-encoding-stats to build encodings (#35758)



### Rationale for this change

This patch uses `encoding_stats` to build the encodings. Currently, `ColumnChunk.encodings` is repeated ( May has multiple `PLAIN` ) and having some wired logic by getting `WriterProperties`. And if later we want to support Fallback to non "PLAIN" encoding, `encoding_stats` would be right, but `encoding` would be "PLAIN". So this patch using `encoding_stats` to build the `encoding`, and force them to be consistent.

### What changes are included in this PR?

### Are these changes tested?

Already has test

### Are there any user-facing changes?

Some behavior would be changed, but I think my change is right :)

* Closes: #35757

Lead-authored-by: mwish <maplewish117@gmail.com>
Co-authored-by: Antoine Pitrou <pitrou@free.fr>
Co-authored-by: Gang Wu <ustcwg@gmail.com>
Signed-off-by: Antoine Pitrou <antoine@python.org>