Windows: Abstracted out `os::name_job` in stout.
Windows: Abstracted out `os::name_job` in stout.

Almost all uses identify a job object by the PID, but the job object
handle must be obtained by name. So this overloads `os::open_job` to
call `os::name_job` when given a PID.

Review: https://reviews.apache.org/r/63275

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