[dotnet] Deprecate saving screenshots with different image formats (#…

…12878)

* Deprecate saving screenshots with different image formats

---------

Co-authored-by: Titus Fortner <titusfortner@users.noreply.github.com>

dotnet/src/webdriver/Screenshot.cs

@@ -26,6 +26,7 @@ namespace OpenQA.Selenium
  /// <summary>
  /// File format for saving screenshots.
  /// </summary>
+ [Obsolete("Support for decoding/encoding between different image formats is deprecated")]
  public enum ScreenshotImageFormat
  {
  /// <summary>
@@ -84,6 +85,7 @@ public override void SaveAsFile(string fileName)
  /// <param name="fileName">The full path and file name to save the screenshot to.</param>
  /// <param name="format">A <see cref="ScreenshotImageFormat"/> value indicating the format
  /// to save the image to.</param>
+ [Obsolete("Support for decoding/encoding between different image formats is deprecated; use SaveAsFile(string fileName) method instead")]
  public void SaveAsFile(string fileName, ScreenshotImageFormat format)
  {
  using (MemoryStream imageStream = new MemoryStream(this.AsByteArray))