Let ExportForProcess use default ContractType

There's no need to specify a contract interface when exporting a
property.

Author: jcansdale

src/GitHub.Exports/Exports/ExportForProcess.cs

@@ -20,9 +20,9 @@ public sealed class ExportForProcessAttribute : ExportAttribute
         /// <summary>
         /// Define an export that is only exposed in a specific named process.
         /// </summary>
-        /// <param name="contractType">The contract type to expose.</param>
         /// <param name="processName">Name of the process to expose export from (e.g. 'devenv').</param>
-        public ExportForProcessAttribute(Type contractType, string processName) :
+        /// <param name="contractType">The contract type to expose.</param>
+        public ExportForProcessAttribute(string processName, Type contractType = null) :
             base(ContractNameForProcess(contractType, processName), contractType)
         {
             ProcessName = processName;

src/GitHub.VisualStudio/GitHubPackage.cs

@@ -119,19 +119,19 @@ public ServiceProviderExports([Import(typeof(SVsServiceProvider))] IServiceProvi
             this.serviceProvider = serviceProvider;
         }
 
-        [ExportForProcess(typeof(ILoginManager), ProcessName)]
+        [ExportForProcess(ProcessName)]
         public ILoginManager LoginManager => GetService<ILoginManager>();
 
-        [ExportForProcess(typeof(IGitHubServiceProvider), ProcessName)]
+        [ExportForProcess(ProcessName)]
         public IGitHubServiceProvider GitHubServiceProvider => GetService<IGitHubServiceProvider>();
 
-        [ExportForProcess(typeof(IUsageTracker), ProcessName)]
+        [ExportForProcess(ProcessName)]
         public IUsageTracker UsageTracker => GetService<IUsageTracker>();
 
-        [ExportForProcess(typeof(IVSGitExt), ProcessName)]
+        [ExportForProcess(ProcessName)]
         public IVSGitExt VSGitExt => GetService<IVSGitExt>();
 
-        [ExportForProcess(typeof(IPackageSettings), ProcessName)]
+        [ExportForProcess(ProcessName)]
         public IPackageSettings PackageSettings => GetService<IPackageSettings>();
 
         T GetService<T>() => (T)serviceProvider.GetService(typeof(T));