[I] [C++][Parquet] Revisit is_sorted flag in Parquet DictionaryPageHeader [arrow]

["mapleFU (via GitHub)" <gi...@apache.org>]

mapleFU opened a new issue, #40948:
URL: https://github.com/apache/arrow/issues/40948

   ### Describe the enhancement requested
   
   Parquet-format has dictionary `is_sorted` flag. However, seems no impl enables this. `is_sorted` is useful when input data is ordered and building filter on dictionary. It could make "dictionary filter" fast(without building a hashtable).
   
   This requires set `is_sorted` flag during writing dictionary page. We can fast checking it if the dict is sorted. Like:
   
   ```
   WriteBatchToDict(RecordBatch) {
     if (is_sorted) {
       is_sorted = checkDict(RecordBatch)
     }
     // do write
   }
   ```
   
   [1] https://github.com/apache/parquet-format/blob/master/src/main/thrift/parquet.thrift#L613-L614
   
   ### Component(s)
   
   C++, Parquet


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