Add an a image comparer

[mattleibow]

Description of Change

Add an API to generate image diffs. This is pretty basic with just a difference being used in each channel, but is surprisingly simple and accurate.

Bugs Fixed

None.

API Changes

public static class SKPixelComparer
{
	public static SKPixelComparisonResult Compare(SKBitmap first, SKBitmap second);
	public static SKPixelComparisonResult Compare(SKPixmap first, SKPixmap second);
	public static SKPixelComparisonResult Compare(SKImage first, SKImage second);
	public static SKPixelComparisonResult Compare(SKBitmap first, SKBitmap second, SKBitmap mask);
	public static SKPixelComparisonResult Compare(SKPixmap first, SKPixmap second, SKPixmap mask);
	public static SKPixelComparisonResult Compare(SKImage first, SKImage second, SKImage mask);
	public static SKImage GenerateDifferenceMask(SKBitmap first, SKBitmap second);
	public static SKImage GenerateDifferenceMask(SKPixmap first, SKPixmap second);
	public static SKImage GenerateDifferenceMask(SKImage first, SKImage second);
}

public class SKPixelComparisonResult
{
	public SKPixelComparisonResult(int totalPixels, int errorPixelCount, int absoluteError);
	public int TotalPixels { get; }
	public int ErrorPixelCount { get; }
	public double ErrorPixelPercentage { get; }
	public int AbsoluteError { get; }
}

Behavioral Changes

None. All new APIs.

PR Checklist

• Has tests (if omitted, state reason in description)
• Has samples (if omitted, state reason in description)
• Rebased on top of main at time of PR
• Changes adhere to coding standard
• Updated documentation