[C++/Python] Add Decimal Parquet Read/Write Tests

[asfimport]

Reporter: Phillip Cloud / @cpcloud
Assignee: Phillip Cloud / @cpcloud

Related issues:

• [Python] No support reading columns of type decimal(19,4) (is depended upon by)

PRs and other links:

• GitHub Pull Request #1335

_{Note: This issue was originally created as ARROW-1839. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
Issue resolved by pull request 1335
#1335