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GH-42100: [C++][Parquet] ParquetFilePrinter::JSONPrint print length of FLBA (#41981)



### Rationale for this change

Print FLBA length in `ParquetFilePrinter::JSONPrint`

### What changes are included in this PR?

Print FLBA length in `ParquetFilePrinter::JSONPrint`

### Are these changes tested?

no need

### Are there any user-facing changes?

no

* GitHub Issue: #42100

Authored-by: mwish <maplewish117@gmail.com>
Signed-off-by: mwish <maplewish117@gmail.com>