[C++][Parquet] Support Decimal from Int32/Int64 in StatisticsAsScalars

[wjones127]

Describe the enhancement requested

Once #15244 is merged, we will be able to create these files ourselves, making this easier to test.

Component(s)

C++, Parquet

[mapleFU]

What's the status of this patch? Would you mind me to take it?

[wjones127]

Yes you are welcome to. I won’t get to it soon.