Add BlurHash support to backend

MediaBrowser.Controller/Drawing/IImageEncoder.cs

@@ -43,6 +43,13 @@ namespace MediaBrowser.Controller.Drawing
         /// <returns>The image dimensions.</returns>
         ImageDimensions GetImageSize(string path);
 
+        /// <summary>
+        /// Get the blurhash of an image.
+        /// </summary>
+        /// <param name="path">The filepath of the image.</param>
+        /// <returns>The blurhash.</returns>
+        string GetImageHash(string path);
+
         /// <summary>
         /// Encode an image.
         /// </summary>