[C++] Add facility to get current thread id

[asfimport]

Reporter: Antoine Pitrou / @pitrou
Assignee: Antoine Pitrou / @pitrou

PRs and other links:

• GitHub Pull Request #10644

_{Note: This issue was originally created as ARROW-13244. Please see the migration documentation for further details.}

[asfimport]

Antoine Pitrou / @pitrou:
Issue resolved by pull request 10644
#10644