Fix startup perf.

Microsoft.Toolkit.Win32.UI.XamlHost/MetadataProviderDiscovery.cs

@@ -73,7 +73,20 @@ namespace Microsoft.Toolkit.Win32.UI.XamlHost
             // Reflection-based runtime metadata probing
             var currentDirectory = new FileInfo(typeof(MetadataProviderDiscovery).Assembly.Location).Directory;
 
-            foreach (var file in currentDirectory.EnumerateFiles("*.exe").Union(currentDirectory.EnumerateFiles("*.dll")))
+            foreach (var assembly in GetAssemblies(currentDirectory, "*.exe"))
+            {
+                yield return assembly;
+            }
+
+            foreach (var assembly in GetAssemblies(currentDirectory, "*.dll"))
+            {
+                yield return assembly;
+            }
+        }
+
+        private static IEnumerable<Assembly> GetAssemblies(DirectoryInfo folder, string fileFilter)
+        {
+            foreach (var file in folder.EnumerateFiles(fileFilter))
             {
                 Assembly a = null;
 

Microsoft.WinRT.Win32.targets

@@ -12,7 +12,7 @@
       <CreateItem Include="%(BuildOutputPaths.Identity)">
         <Output ItemName="BuildOutputs" TaskParameter="Include"/>
       </CreateItem>
-      <CreateItem Include="%(BuildOutputs.RelativeDir)*.dll;%(BuildOutputs.RelativeDir)*.xbf;%(BuildOutputs.RelativeDir)*.pri">
+      <CreateItem Include="%(BuildOutputs.RelativeDir)*.exe;%(BuildOutputs.RelativeDir)*.dll;%(BuildOutputs.RelativeDir)*.xbf;%(BuildOutputs.RelativeDir)*.pri">
         <Output ItemName="Filter" TaskParameter="Include"/>
       </CreateItem>
       <CreateItem Include="%(BuildOutputs.RelativeDir)AppxManifest*.xml">