[release/10.0.4xx] Add dotnet test --results-directory-layout

src/Cli/Microsoft.DotNet.Cli.Definitions/CommandDefinitionStrings.resx

@@ -555,6 +555,14 @@ This is equivalent to deleting project.assets.json.</value>
     <value>The directory where the test results will be placed.
 The specified directory will be created if it does not exist.</value>
   </data>
+  <data name="CmdResultsDirectoryLayoutDescription" xml:space="preserve">
+    <value>Specifies how test results are organized within the results directory.
+'flat' (the default) places the results of every test project directly in the results directory.
+'per-module' gives every test project its own '&lt;project&gt;/&lt;target-framework&gt;_&lt;runtime&gt;' subdirectory, so reports with the same file name cannot overwrite each other.</value>
+  </data>
+  <data name="CmdResultsDirectoryLayoutName" xml:space="preserve">
+    <value>LAYOUT</value>
+  </data>
   <data name="CmdConfigFileDescription" xml:space="preserve">
     <value>Specifies a testconfig.json file.</value>
   </data>

src/Cli/Microsoft.DotNet.Cli.Definitions/Commands/Test/TestCommandDefinition.MicrosoftTestingPlatform.cs

@@ -46,6 +46,13 @@ public sealed class MicrosoftTestingPlatform : TestCommandDefinition, ICustomHel
             Arity = ArgumentArity.ExactlyOne
         };
 
+        public readonly Option<string> ResultsDirectoryLayoutOption = new Option<string>("--results-directory-layout")
+        {
+            Description = CommandDefinitionStrings.CmdResultsDirectoryLayoutDescription,
+            HelpName = CommandDefinitionStrings.CmdResultsDirectoryLayoutName,
+            Arity = ArgumentArity.ExactlyOne
+        }.AcceptOnlyFromAmong("flat", "per-module");
+
         public const string ConfigFileOptionName = "--config-file";
 
         public readonly Option<string> ConfigFileOption = new(ConfigFileOptionName)
@@ -140,6 +147,7 @@ public MicrosoftTestingPlatform()
             Options.Add(TestModulesFilterOption);
             Options.Add(TestModulesRootDirectoryOption);
             Options.Add(ResultsDirectoryOption);
+            Options.Add(ResultsDirectoryLayoutOption);
             Options.Add(ConfigFileOption);
             Options.Add(DiagnosticOutputDirectoryOption);
             Options.Add(MaxParallelTestModulesOption);

src/Cli/dotnet/Commands/Test/MTP/MSBuildHandler.cs

@@ -74,6 +74,9 @@ public void EnqueueTestApplications(TestApplicationActionQueue queue)
         }
     }
 
+    public IEnumerable<TestModule> EnumerateTestModules()
+        => _testApplications.SelectMany(static moduleGroup => moduleGroup);
+
     private static void LogProjectProperties(IEnumerable<ParallelizableTestModuleGroupWithSequentialInnerModules> moduleGroups)
     {
         if (!Logger.TraceEnabled)