[tests] Fix PlatformDetection.IsMonoInterpreter for mobile (#59587)

* [tests] Correctly detect the Mono interpreter

Checking for MONO_ENV_OPTIONS is not reliable for the mobile test runners
because they use the embedding API to enable the interpreter, rather than
setting an environment option.

Instead detect the interpreter by checking the values of the
IsDynamicCodeSupported and IsDynamicCodeCompiled runtime features.

* [tests] Run System.Threading.Tasks.Dataflow.Tests on Apple platforms

* Only check RuntimeFeature on netcoreapp.  Otherwise return false

these tests are not running on mono if they're running on .NET Framework

src/libraries/Common/tests/TestUtilities/System/PlatformDetection.cs

@@ -467,13 +467,10 @@ private static bool GetTls13Support()
         private static bool GetIsRunningOnMonoInterpreter()
         {
 #if NETCOREAPP
-            if (IsBrowser)
-                return RuntimeFeature.IsDynamicCodeSupported;
+            return IsMonoRuntime && RuntimeFeature.IsDynamicCodeSupported && !RuntimeFeature.IsDynamicCodeCompiled;
+#else
+            return false;
 #endif
-            // This is a temporary solution because mono does not support interpreter detection
-            // within the runtime.
-            var val = Environment.GetEnvironmentVariable("MONO_ENV_OPTIONS");
-            return (val != null && val.Contains("--interpreter"));
         }
 
         private static bool GetIsBrowserDomSupported()

src/libraries/tests.proj

@@ -170,7 +170,6 @@
     <ProjectExclusions Include="$(RepoRoot)/src/tests/FunctionalTests/tvOS/Simulator/AOT/tvOS.Simulator.Aot.Test.csproj" />
     <!-- Crashes randomly during test runs https://github.com/dotnet/runtime/issues/52460 -->
     <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.Threading.Tasks\tests\System.Threading.Tasks.Tests.csproj" />
-    <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.Threading.Tasks.Dataflow\tests\System.Threading.Tasks.Dataflow.Tests.csproj" />
 
     <!-- Crash https://github.com/dotnet/runtime/issues/56085 -->
     <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.Text.Json/tests/System.Text.Json.SourceGeneration.Tests/System.Text.Json.SourceGeneration.Roslyn3.11.Tests.csproj" />