Imported Upstream version 6.0.0.172

Former-commit-id: f3cc9b82f3e5bd8f0fd3ebc098f789556b44e9cd

mcs/class/System.Core/System.IO.Pipes/PipeStream.NotSupported.cs

@@ -52,7 +52,10 @@ namespace System.IO.Pipes
 
 		internal virtual void DisposeCore(bool disposing)
 		{
-			throw new PlatformNotSupportedException();
+			// It's incorrect to throw PNSE here because the finalizer will invoke DisposeCore.
+			// The finalizer can be hit if someone attempts to construct a PipeStream
+			//  because the failed constructor invocation still creates an instance and registers
+			//  it for finalization.
 		}
 
 		private unsafe int ReadCore(Span<byte> buffer)