Change AverageBytesPerMb to ReadOnlySpan<byte>

Author: brianpopow

src/ImageSharp/Formats/Webp/Lossy/Vp8Encoder.cs

@@ -73,8 +73,6 @@ internal class Vp8Encoder : IDisposable
 
         private readonly bool alphaCompression;
 
-        private readonly byte[] averageBytesPerMb = { 50, 24, 16, 9, 7, 5, 3, 2 };
-
         private const int NumMbSegments = 4;
 
         private const int MaxItersKMeans = 6;
@@ -174,6 +172,9 @@ public Vp8Encoder(
             this.ResetBoundaryPredictions();
         }
 
+        // This uses C#'s optimization to refer to the static data segment of the assembly, no allocation occurs.
+        private static ReadOnlySpan<byte> AverageBytesPerMb => new byte[] { 50, 24, 16, 9, 7, 5, 3, 2 };
+
         public int BaseQuant { get; set; }
 
         /// <summary>
@@ -319,7 +320,7 @@ public void Encode<TPixel>(Image<TPixel> image, Stream stream)
             this.SetLoopParams(this.quality);
 
             // Initialize the bitwriter.
-            int averageBytesPerMacroBlock = this.averageBytesPerMb[this.BaseQuant >> 4];
+            int averageBytesPerMacroBlock = AverageBytesPerMb[this.BaseQuant >> 4];
             int expectedSize = this.Mbw * this.Mbh * averageBytesPerMacroBlock;
             this.bitWriter = new Vp8BitWriter(expectedSize, this);