PR Summary

Currently, when the Pipeline is being cleaned up, we call Process.Dispose() with the intent to kill any running processes. However, Dispose() only closes the redirected streams and thus has different behavior on Windows, Linux, and macOS. On Linux, it appears that the processes will be killed by the OS. However, on macOS, the process continues to run in the background. On Windows, because of the difference of exe vs winexe (graphical apps), we can't forcibly kill the process as starting notepad would be killed instantly so we leave it as Dispose().

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