improvve PolygonScanning.MD and add benchmark results

Author: antonfirsov

src/ImageSharp.Drawing/Shapes/Rasterization/PolygonScanning.MD

@@ -26,7 +26,7 @@ SCANLINE 2 >>>> | >>>>>>>>>>>>>> + - - - - - - - - - - +      >>>>>>>>>
                 |                |               
                 |              D |
                 |                |
-                |                |
+                | (1)            | (1)
                 +  - - - - - - - +
 
 ```
@@ -36,14 +36,14 @@ SCANLINE 2 >>>> | >>>>>>>>>>>>>> + - - - - - - - - - - +      >>>>>>>>>
 
 - Intersection with edge A is trivial, since it's being intersected on an internal point of the edge
 - The second intersection is more tricky: the intersection point is at the connection (vertex) between edges B and C, but we do not want to emit the intersection 2 times.
-  - To avoid this, when checking the scanline's collision against edge B we emit 0 intersections for edge B at it's endpoint (Y1), when checking against edge C we emit 1 point at its start point (Y0)
+  - To avoid this, when checking the scanline's collision against edge B we emit 0 intersections at it's endpoint (Y1), when checking against edge C we emit 1 point at its start point (Y0)
 
 #### Intersections at SCANLINE 2
 
 - Intersection with edge A is trivial, since it's being intersected on an internal point
 - However the rest is tricky: We want to to emulate the intersection with the collinear edge X not being listed in `ScanEdgeCollection`.
   - The easiest way is to emit a point pair for the line part between A-D and a second point pair for D-C (to emulate the intersection with X)
-  - To achieve this, we should emit the start point (Y0) intersection of the D edge 2 times!
+  - To achieve this, we should emit the start point (Y0) of the D edge 2 times when intersecting it!
 
 ### Edge emit rules
 

tests/ImageSharp.Drawing.Benchmarks/Drawing/FillPolygon.cs

@@ -147,6 +147,20 @@ protected override PointF[][] GetPoints(FeatureCollection features)
                                   * Matrix3x2.CreateScale(60, 60);
             return PolygonFactory.GetGeoJsonPoints(state, transform).ToArray();
         }
+        
+        // ** 11/13/2020 @ Anton's PC ***
+        // BenchmarkDotNet=v0.12.1, OS=Windows 10.0.18363.1198 (1909/November2018Update/19H2)
+        // Intel Core i7-7700HQ CPU 2.80GHz (Kaby Lake), 1 CPU, 8 logical and 4 physical cores
+        //     .NET Core SDK=5.0.100-preview.6.20318.15
+        // [Host]     : .NET Core 3.1.1 (CoreCLR 4.700.19.60701, CoreFX 4.700.19.60801), X64 RyuJIT
+        // DefaultJob : .NET Core 3.1.1 (CoreCLR 4.700.19.60701, CoreFX 4.700.19.60801), X64 RyuJIT
+        //
+        //
+        // |        Method |       Mean |    Error |    StdDev | Ratio | RatioSD |
+        // |-------------- |-----------:|---------:|----------:|------:|--------:|
+        // | SystemDrawing |   457.4 us |  9.07 us |  23.40 us |  2.15 |    0.10 |
+        // |    ImageSharp | 3,079.5 us | 61.45 us | 138.71 us | 14.30 |    0.89 |
+        // |     SkiaSharp |   217.7 us |  4.29 us |   6.55 us |  1.00 |    0.00 |
     }
 
     public class FillPolygonSmall : FillPolygon