[C++] Expose Arrow's plan execution helpers (Finishes, ResultWith)

### Describe the enhancement requested

Branching off from https://github.com/apache/arrow/issues/33538, it would probably be generally useful for people building on top of libarrow to have helpers such as ~~`StartAndCollect`~~, `Finishes`, and `ResultWith` be part of the public API. There may be other related helpers in this category that that may be useful.

### Component(s)

C++

Edit: Removed StartAndCollect as requested in https://github.com/apache/arrow/issues/34083#issuecomment-1423538006.

Start with the related discussion in issue 33538 and inspect the current definitions and visibility of Finishes and ResultWith in the C++ execution-plan code. Determine which execution helpers belong in libarrow's public API, then verify that callers building on libarrow can use the exposed helpers and that the existing behavior remains covered by the relevant tests.

Written by the indexing model from the issue text.