[C++] Implement OptionalParallelForAsync

[asfimport]

In ARROW-11843 we found that we still can't enable parallel column conversion for Parquet datasets because the Arrow Parquet reader uses OptionalParallelFor, which does a parallel wait. We should provide an async version to avoid nested parallelism.

Reporter: David Li / @lidavidm
Assignee: David Li / @lidavidm

Related issues:

• [C++][Parquet] Always transfer to executor in Parquet AsyncGenerator (is duplicated by)
• [C++] Add asynchronous read to parquet::arrow::FileReader (relates to)

PRs and other links:

• GitHub Pull Request #10482

_{Note: This issue was originally created as ARROW-12597. Please see the migration documentation for further details.}

[asfimport]

David Li / @lidavidm:
Issue resolved by pull request 10482
#10482