[C++] Finish implementation of scalar types for Duration and Interval

[asfimport]

Once #3644 is checked in these types should be completed.

Reporter: Micah Kornfield / @emkornfield
Assignee: Micah Kornfield / @emkornfield

PRs and other links:

• GitHub Pull Request #4721

_{Note: This issue was originally created as ARROW-5261. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
Issue resolved by pull request 4721
#4721