Fix dotnet run double dash passing arguments

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.

src/dotnet/commands/dotnet-run/RunCommand.cs

@@ -13,11 +13,11 @@ namespace Microsoft.DotNet.Tools.Run
 {
     public partial class RunCommand
     {
-        public string Configuration { get; set; }
-        public string Framework { get; set; }
-        public bool NoBuild { get; set; }
-        public string Project { get; set; }
-        public IReadOnlyCollection<string> Args { get; set; }
+        public string Configuration { get; private set; }
+        public string Framework { get; private set; }
+        public bool NoBuild { get; private set; }
+        public string Project { get; private set; }
+        public IReadOnlyCollection<string> Args { get; private set; }
 
         private List<string> _args;
         private bool ShouldBuild => !NoBuild;
@@ -38,6 +38,34 @@ namespace Microsoft.DotNet.Tools.Run
                 .ExitCode;
         }
 
+        public RunCommand(string configuration,
+            string framework,
+            bool noBuild,
+            string project,
+            IReadOnlyCollection<string> args)
+        {
+            Configuration = configuration;
+            Framework = framework;
+            NoBuild = noBuild;
+            Project = project;
+            Args = args;
+        }
+
+        public RunCommand MakeNewWithReplaced(string configuration = null,
+            string framework = null,
+            bool? noBuild = null,
+            string project = null,
+            IReadOnlyCollection<string> args = null)
+        {
+            return new RunCommand(
+                configuration ?? this.Configuration,
+                framework ?? this.Framework,
+                noBuild ?? this.NoBuild,
+                project ?? this.Project,
+                args ?? this.Args
+            );
+        }
+
         private void EnsureProjectIsBuilt()
         {
             List<string> buildArgs = new List<string>();