Implements support for backgrounding pipelines with &. Putting & at the end of a pipeline will cause the pipeline
to be run as a PowerShell job. When a pipeline is backgrounded a job object is returned. Once the pipeline is
running as a job, all of the normal job cmdlets can be used to manage the job. Variables (ignoring process-specific
variables) used in the pipeline are automatically copied to the job so
copy $foo $bar &
just works. The job is also run in the current directory instead of the user's home directory as is the case with Start-Job.Implement
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