Update NUnit to 3.16.1

Source/Platforms/DotNet/NUnit/nunit3-console.exe.config

@@ -1,12 +1,29 @@
 <?xml version="1.0" encoding="utf-8"?>
 <configuration>
+  <!--
+   The console runner runs under .NET 2.0 or higher. 
+   The setting useLegacyV2RuntimeActivationPolicy only applies 
+   under .NET 4.0 and permits use of mixed mode assemblies, 
+   which would otherwise not load correctly.
+  -->
   <startup useLegacyV2RuntimeActivationPolicy="true">
     <supportedRuntime version="v4.0.30319" />
+    <supportedRuntime version="v2.0.50727" />
   </startup>
   <runtime>
+    <!-- Ensure that test exceptions don't crash NUnit -->
     <legacyUnhandledExceptionPolicy enabled="1" />
+    <!--
+     Since legacyUnhandledExceptionPolicy keeps the console from being killed even though an NUnit framework
+     test worker thread is killed, this is needed to prevent a hang. NUnit framework can only handle these
+     exceptions when this config element is present. (Or if future versions of NUnit framework drop support
+     for partial trust which would enable it to use [HandleProcessCorruptedStateExceptions].)
+    -->
     <legacyCorruptedStateExceptionsPolicy enabled="true" />
+    <!-- Run partial trust V2 assemblies in full trust under .NET 4.0 -->
     <loadFromRemoteSources enabled="true" />
+    <!-- Enable reading source information from Portable and Embedded PDBs when running applications -->
+    <!-- built against previous .NET Framework versions on .NET Framework 4.7.2 -->
     <AppContextSwitchOverrides value="Switch.System.Diagnostics.IgnorePortablePDBsInStackTraces=false" />
   </runtime>
 </configuration>