Debugging tests with a native debugger requires --InIsolation flag

[ocitrev]

With environment variable VSTEST_HOST_NATIVE_DEBUG, we can use a native debugger to debug tests but it requires --InIsolation flag.
When using the argument --tests: to run a specific test, testhost.exe is spawned twice and we must attach twice to properly debug.

When the environment variable VSTEST_RUNNER_DEBUG is set, vstest.console only waits for a managed debugger.

I propose to add new environment variable VSTEST_RUNNER_NATIVE_DEBUG to enable native debugging of vstest.conssole.
This will enable native debugging of tests without the --InIsolation flag.

The proposed code changes

diff --git a/src/vstest.console/CommandLine/Executor.cs b/src/vstest.console/CommandLine/Executor.cs
index 951a4166..a153dd49 100644
--- a/src/vstest.console/CommandLine/Executor.cs
+++ b/src/vstest.console/CommandLine/Executor.cs
@@ -91,6 +91,7 @@ internal class Executor
     internal Executor(IOutput output, ITestPlatformEventSource testPlatformEventSource, IProcessHelper processHelper, IEnvironment environment)
     {
         DebuggerBreakpoint.AttachVisualStudioDebugger(WellKnownDebugEnvironmentVariables.VSTEST_RUNNER_DEBUG_ATTACHVS);
+        DebuggerBreakpoint.WaitForNativeDebugger(WellKnownDebugEnvironmentVariables.VSTEST_RUNNER_NATIVE_DEBUG);
         DebuggerBreakpoint.WaitForDebugger(WellKnownDebugEnvironmentVariables.VSTEST_RUNNER_DEBUG);
 
         Output = output;

diff --git a/src/Microsoft.TestPlatform.Execution.Shared/WellKnownDebugEnvironmentVariables.cs b/src/Microsoft.TestPlatform.Execution.Shared/WellKnownDebugEnvironmentVariables.cs
index 83402bce..61fe4fa0 100644
--- a/src/Microsoft.TestPlatform.Execution.Shared/WellKnownDebugEnvironmentVariables.cs
+++ b/src/Microsoft.TestPlatform.Execution.Shared/WellKnownDebugEnvironmentVariables.cs
@@ -13,4 +13,5 @@ internal static class WellKnownDebugEnvironmentVariables
     public const string VSTEST_HOST_DEBUG_ATTACHVS = nameof(VSTEST_HOST_DEBUG_ATTACHVS);
     public const string VSTEST_RUNNER_DEBUG_ATTACHVS = nameof(VSTEST_RUNNER_DEBUG_ATTACHVS);
     public const string VSTEST_HOST_NATIVE_DEBUG = nameof(VSTEST_HOST_NATIVE_DEBUG);
+    public const string VSTEST_RUNNER_NATIVE_DEBUG = nameof(VSTEST_RUNNER_NATIVE_DEBUG);
 }

[nohwnd]

Sure, please go ahead and make a PR.