[Concurrency] Bring back ability to get a queue custom executor in executorForEnqueuedJob#81198

ktoso wants to merge 2 commits intoswiftlang:mainswiftlang/swift:mainfrom

ktoso:wip-bring-back-queue-executorForEnqueuedJobktoso/swift:wip-bring-back-queue-executorForEnqueuedJobCopy head branch name to clipboard