[ARROW-1519] [C++] Move DecimalUtil functions to methods on the Int128 class

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 0.6.0
• Fix Version/s: 0.7.0
• Component/s: C++
• External issue URL: https://github.com/apache/arrow/issues/17536
• Assignee: Phillip Cloud
• Reporter: Phillip Cloud
• Created: 10/Sep/17 21:10
• Updated: 11/Jan/23 07:15
• Resolved: 12/Sep/17 01:49