Add built-in ThumbnailViewer plugin

QuickLook.Plugin/QuickLook.Plugin.ThumbnailViewer/Helper.cs

@@ -0,0 +1,20 @@
+using System.IO;
+using System.Windows.Media.Imaging;
+
+namespace QuickLook.Plugin.ThumbnailViewer;
+
+internal static class Helper
+{
+    public static BitmapImage ReadAsBitmapImage(this Stream imageData)
+    {
+        imageData.Seek(0U, SeekOrigin.Begin);
+
+        BitmapImage bitmap = new();
+        bitmap.BeginInit();
+        bitmap.CacheOption = BitmapCacheOption.OnLoad;
+        bitmap.StreamSource = imageData;
+        bitmap.EndInit();
+        bitmap.Freeze();
+        return bitmap;
+    }
+}