ARROW-13136 adds a coalesce kernel. Use this to implement a binding for the dplyr function coalesce().

Reporter: Ian Cook / @ianmcook
Assignee: Ian Cook / @ianmcook

Related issues:

• [C++] Add option to coalesce kernel to treat NaN as null (is related to)
• [C++] Add a "coalesce" variadic scalar kernel (depends upon)

PRs and other links:

• GitHub Pull Request #10751

_{Note: This issue was originally created as ARROW-13201. Please see the migration documentation for further details.}