arrow

GH-34633: [C++][Parquet] Fix StreamReader to read decimals (#34720)

### Rationale for this change

StreamReader only supports reading decimals from int32 and int64. User cannot read decimals from FIXED_LENGTH_BYTE_ARRAY or BYTE_ARRAY.

### What changes are included in this PR?

Support StreamReader to read decimals via arrow::Decimal128 type.

### Are these changes tested?

Added two test cases to read them.

### Are there any user-facing changes?

Yes, now user can directly use arrow::Decimal128 to read from parquet file.
* Closes: #34633

Authored-by: Gang Wu <ustcwg@gmail.com>
Signed-off-by: Weston Pace <weston.pace@gmail.com>