Lazily initialize global service provider and MEF components

Otherwise, the previous approach can hang VS if the cache is being rebuilt
and we're requesting it synchronously from within the process start.

Note that unless MEF components are requested, we don't even initialize
the component model service at all either.

Fixes #34

src/Xunit.Vsix/GlobalServiceProvider.cs

@@ -14,8 +14,8 @@ namespace Xunit;
 [EditorBrowsable(EditorBrowsableState.Never)]
 public static class GlobalServiceProvider
 {
-    static readonly IServiceProvider instance;
-    static readonly dynamic components;
+    static readonly System.IServiceProvider instance;
+    static readonly Lazy<dynamic> components;
 
     static GlobalServiceProvider()
     {
@@ -30,8 +30,10 @@ static GlobalServiceProvider()
             else
             {
                 instance = new OleServiceProvider(dte);
-                components = instance.GetService<Interop.SComponentModel, object>().AsDynamicReflection();
             }
+
+            components = new Lazy<dynamic>(() => 
+                instance.GetService<Interop.SComponentModel, object>().AsDynamicReflection());
         }
         catch (NotSupportedException)
         {
@@ -64,12 +66,12 @@ static GlobalServiceProvider()
     /// <summary>
     /// Retrieves an exported MEF component from the currently running Visual Studio.
     /// </summary>
-    public static T GetExport<T>() => components == null ? null : components?.GetService<T>();
+    public static T GetExport<T>() => components == null ? null : components.Value?.GetService<T>();
 
     /// <summary>
     /// Retrieves exported MEF components from the currently running Visual Studio.
     /// </summary>
-    public static IEnumerable<T> GetExports<T>() => components?.GetExtensions<T>() ?? Array.Empty<T>();
+    public static IEnumerable<T> GetExports<T>() => components.Value?.GetExtensions<T>() ?? Array.Empty<T>();
 
     class NullServices : IServiceProvider
     {

src/Xunit.Vsix/VsClient.cs

@@ -320,7 +320,7 @@ bool Start()
 
             // Retrieve the component model service, which could also now take time depending on new
             // extensions being installed or updated before the first launch.
-            var components = services.GetService<Interop.SComponentModel, object>();
+            //var components = services.GetService<Interop.SComponentModel, object>();
 
             //if (Debugger.IsAttached)
             //{

src/Xunit.Vsix/VsRemoteRunner.cs

@@ -26,6 +26,7 @@ class VsRemoteRunner : MarshalByRefObject, IVsRemoteRunner
     {
         string _pipeName;
         IChannel _channel;
+        IServiceProvider _services;
 
         Dictionary<Type, object> _assemblyFixtureMappings = new Dictionary<Type, object>();
         Dictionary<Type, object> _collectionFixtureMappings = new Dictionary<Type, object>();
@@ -55,6 +56,10 @@ public string[][] GetEnvironment()
 
         public VsixRunSummary Run(VsixTestCase testCase, IMessageBus messageBus)
         {
+            // Before the first test is run, ensure we have initialized the global services 
+            // which in turn requests the component model which ensures MEF is initialized.
+            _services ??= GlobalServiceProvider.Default;
+
             messageBus.QueueMessage(new DiagnosticMessage("Running {0}", testCase.DisplayName));
 
             var aggregator = new ExceptionAggregator();