Add JPEG XL format

src/ImageSharp/Formats/Jxl/JxlFormat.cs

@@ -0,0 +1,17 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using System.Collections.Generic;
+
+namespace SixLabors.ImageSharp.Formats.Jxl;
+
+internal class JxlFormat : IImageFormat
+{
+    public string Name => "JPEG XL";
+
+    public string DefaultMimeType => "image/jxl";
+
+    IEnumerable<string> IImageFormat.MimeTypes => new[] { "image/jxl" };
+
+    IEnumerable<string> IImageFormat.FileExtensions => new[] { "jxl" };
+}