Default alpha compression to true

src/ImageSharp/Formats/Webp/IWebpEncoderOptions.cs

@@ -31,6 +31,7 @@ namespace SixLabors.ImageSharp.Formats.Webp
 
         /// <summary>
         /// Gets a value indicating whether the alpha plane should be compressed with Webp lossless format.
+        /// Defaults to true.
         /// </summary>
         bool UseAlphaCompression { get; }
 

src/ImageSharp/Formats/Webp/WebpEncoder.cs

@@ -24,7 +24,7 @@ namespace SixLabors.ImageSharp.Formats.Webp
         public WebpEncodingMethod Method { get; set; } = WebpEncodingMethod.Default;
 
         /// <inheritdoc/>
-        public bool UseAlphaCompression { get; set; }
+        public bool UseAlphaCompression { get; set; } = true;
 
         /// <inheritdoc/>
         public int EntropyPasses { get; set; } = 1;

src/ImageSharp/Formats/Webp/WebpEncoderCore.cs

@@ -23,6 +23,7 @@ namespace SixLabors.ImageSharp.Formats.Webp
 
         /// <summary>
         /// Indicating whether the alpha plane should be compressed with Webp lossless format.
+        /// Defaults to true.
         /// </summary>
         private readonly bool alphaCompression;