text fixes, remove file existence validations from parse

src/dotnet/CommonOptions.cs

@@ -64,41 +64,5 @@ namespace Microsoft.DotNet.Cli
 
         public static ArgumentsRule DefaultToCurrentDirectory(this ArgumentsRule rule) =>
             rule.With(defaultValue: () => PathUtility.EnsureTrailingSlash(Directory.GetCurrentDirectory()));
-
-        public static ArgumentsRule ExistingFilesOnly(
-            this ArgumentsRule rule) =>
-            rule.And(new ArgumentsRule(o =>
-            {
-                foreach (var filePath in o.Arguments)
-                {
-                    if (!File.Exists(filePath) &&
-                        !Directory.Exists(filePath))
-                    {
-                        return $"File not found: {filePath}";
-                    }
-                }
-
-                return null;
-            }));
-
-        public static ArgumentsRule ExistingSlnFileOrDirectoryOnly(
-            this ArgumentsRule rule) =>
-            rule
-                .ExistingFilesOnly()
-                .And(new ArgumentsRule(o =>
-                {
-                    foreach (var path in o.Arguments)
-                    {
-                        if (path.HasExtension(".sln") || 
-                        path.IsDirectory())
-                        {
-                            continue;
-                        }
-
-                        return $"Specified path '{path}' is not a directory or solution file.";
-                    }
-
-                    return null;
-                }));
     }
 }

src/dotnet/commands/dotnet-add/AddCommandParser.cs

@@ -19,7 +19,6 @@ namespace Microsoft.DotNet.Cli
                 "add",
                 ".NET Add Command",
                 Accept.ExactlyOneArgument()
-                      .ExistingFilesOnly()
                       .DefaultToCurrentDirectory()
                       .With(name: "PROJECT",
                             description: "The project file to operate on. If a file is not specified, the command will search the current directory for one."),

test/dotnet-add-reference.Tests/GivenDotnetAddReference.cs

@@ -112,8 +112,8 @@ Options:
                     .WithProject("one two three")
                     .Execute("proj.csproj");
             cmd.ExitCode.Should().NotBe(0);
-            cmd.StdErr.Should().Be("Unrecognized command or argument 'two'");
+            cmd.StdErr.Should().BeVisuallyEquivalentTo(
-            cmd.StdOut.Should().Be("Specify --help for a list of available options and commands.");
+                "Unrecognized command or argument 'two'\r\nUnrecognized command or argument 'three'");
         }
 
         [Theory]

test/dotnet-list-reference.Tests/GivenDotnetListReference.cs

@@ -57,7 +57,8 @@ Options:
                     .WithProject("one two three")
                     .Execute("proj.csproj");
             cmd.ExitCode.Should().NotBe(0);
-            cmd.StdErr.Should().Be("Unrecognized command or argument 'two'");
+            cmd.StdErr.Should().BeVisuallyEquivalentTo(
+                "Unrecognized command or argument 'one'\r\nUnrecognized command or argument 'two'\r\nUnrecognized command or argument 'three'");
         }
 
         [Theory]