When run “dotnet run -- foo”, foo should be the argument passed to the
subject app. After replacing the original parser, dotnet-run did not
utilize the “unparsedtoken” of the parsed result.
To append unparsedtoken to RunCommand’s argument is not straight
forward. RunCommand has an “immutable constructor”, which is a good
thing, so I made update RunCommand’s argument following the immutable
pattern -- create a new object with the original field but only change
the arguments. I also made these filed private set.
