[C++] Use self-pipe in signal-receiving StopSource

[asfimport]

The signal-receiving StopSource currently uses elaborate hacks to request the StopSource from a signal handler. Instead we should just use a SelfPipe and send signals to a worker thread.

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

Related issues:

• [C++] Create after-fork facility (relates to)
• [C++] Investigate spawning arbitrary callbacks from StopToken (is depended upon by)

PRs and other links:

• GitHub Pull Request #14250

_{Note: This issue was originally created as ARROW-17859. Please see the migration documentation for further details.}

[asfimport]

Antoine Pitrou / @pitrou:
Issue resolved by pull request 14250
#14250