Argument.AcceptLegalFilePathsOnly should return void

src/System.CommandLine.ApiCompatibility.Tests/ApiCompatibilityApprovalTests.System_CommandLine_api_is_not_changed.approved.txt

@@ -22,7 +22,7 @@ System.CommandLine
     public System.Boolean HasDefaultValue { get; }
     public System.Type ValueType { get; }
     public Argument<T> AcceptLegalFileNamesOnly()
-    public Argument<T> AcceptLegalFilePathsOnly()
+    public System.Void AcceptLegalFilePathsOnly()
     public System.Void AcceptOnlyFromAmong(System.String[] values)
     public System.Void SetDefaultValue(T value)
     public System.Void SetDefaultValueFactory(Func<T> defaultValueFactory)

src/System.CommandLine.Tests/ArgumentTests.cs

@@ -789,8 +789,7 @@ public void Argument_of_enum_can_limit_enum_members_as_valid_values()
         public void Argument_of_T_fluent_APIs_return_Argument_of_T()
         {
             Argument<string> argument = new Argument<string>("--path")
-                .AcceptLegalFileNamesOnly()
-                .AcceptLegalFilePathsOnly();
+                .AcceptLegalFileNamesOnly();
 
             argument.Should().BeOfType<Argument<string>>();
         }

src/System.CommandLine.Tests/ParsingValidationTests.cs

@@ -560,9 +560,11 @@ public class PathValidity
             [Fact]
             public void LegalFilePathsOnly_rejects_command_arguments_containing_invalid_path_characters()
             {
+                Argument<string> argument = new();
+                argument.AcceptLegalFilePathsOnly();
                 var command = new Command("the-command")
                 {
-                    new Argument<string>().AcceptLegalFilePathsOnly()
+                    argument
                 };
 
                 var invalidCharacter = Path.GetInvalidPathChars().First(c => c != '"');
@@ -600,9 +602,11 @@ public void LegalFilePathsOnly_rejects_option_arguments_containing_invalid_path_
             [Fact]
             public void LegalFilePathsOnly_accepts_command_arguments_containing_valid_path_characters()
             {
+                Argument<string[]> argument = new ();
+                argument.AcceptLegalFilePathsOnly();
                 var command = new Command("the-command")
                 {
-                    new Argument<string[]>().AcceptLegalFilePathsOnly()
+                    argument
                 };
 
                 var validPathName = Directory.GetCurrentDirectory();

src/System.CommandLine/Argument{T}.cs

@@ -205,7 +205,7 @@ void UnrecognizedArgumentError(ArgumentResult argumentResult)
         /// Configures the argument to accept only values representing legal file paths.
         /// </summary>
         /// <returns>The configured argument.</returns>
-        public Argument<T> AcceptLegalFilePathsOnly()
+        public void AcceptLegalFilePathsOnly()
         {
             var invalidPathChars = Path.GetInvalidPathChars();
 
@@ -225,8 +225,6 @@ public Argument<T> AcceptLegalFilePathsOnly()
                     }
                 }
             });
-
-            return this;
         }
 
         /// <summary>