This PR adds a "row table" which is a high level API for a 2D structure that has row-major storage. It adds utilities to encode to & from the existing columnar structure via this high level API. Internally it uses RowTableImpl.

It also adds a merge utility that can merge two row tables together.

Reporter: Weston Pace / @westonpace

PRs and other links:

• GitHub Pull Request #13220

_{Note: This issue was originally created as ARROW-16637. Please see the migration documentation for further details.}