There a some differences in support of named pipes for Windows and non-Windows. Named pipes on Unix have a 104 character path limit. On macOS, the `$env:TMPDIR` (on my system) is already 49 characters; corefx adds 12 more. Since AppDomainName isn't really used, changed it from `DefaultAppDomain` to `None` to shorten the name. Need to keep it since Windows PowerShell expects it. Changed `starttime` part of pipe name to 8 hex characters which is to provide uniqueness to the pipe name.
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