[C++] Support order by derived column

[asfimport]

You can't do the equivalent of

SELECT x, y FROM table ORDER BY x * y ASC;

because sorting requires a named column AND because sorting is only done in a SinkNode. You can project to {x, y, x*y} then sort on x*y, but you can't then project back to {x, y} on the sorted data because that's a new ExecPlan and order is not preserved. In R we have to handle this outside of an ExecPlan.

Reporter: Neal Richardson / @nealrichardson

_{Note: This issue was originally created as ARROW-16631. Please see the migration documentation for further details.}