Use ReadOnlySpan

Co-authored-by: Günther Foidl <gue@korporal.at>

src/ImageSharp/Formats/Webp/Lossless/PredictorEncoder.cs

@@ -17,7 +17,8 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossless
     /// </summary>
     internal static unsafe class PredictorEncoder
     {
-        private static readonly sbyte[] DeltaLut = { 16, 16, 8, 4, 2, 2, 2 };
+        // This uses C#'s compiler optimization to refer to assembly's static data directly.
+        private static ReadOnlySpan<sbyte> DeltaLut => new sbyte[] { 16, 16, 8, 4, 2, 2, 2 };
 
         private static readonly sbyte[][] Offset =
         {

src/ImageSharp/Formats/Webp/Lossless/Vp8LEncoder.cs

@@ -85,7 +85,8 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossless
 
         private const int PaletteInvSize = 1 << PaletteInvSizeBits;
 
-        private static readonly byte[] Order = { 1, 2, 0, 3 };
+        // This uses C#'s compiler optimization to refer to assembly's static data directly.
+        private static ReadOnlySpan<byte> Order => new byte[] { 1, 2, 0, 3 };
 
         /// <summary>
         /// Initializes a new instance of the <see cref="Vp8LEncoder"/> class.