Expose GRContext from ISkiaDrawingContextImpl

src/Skia/Avalonia.Skia/DrawingContextImpl.cs

@@ -101,6 +101,7 @@ namespace Avalonia.Skia
         public SKCanvas Canvas { get; }
 
         SKCanvas ISkiaDrawingContextImpl.SkCanvas => Canvas;
+        GRContext ISkiaDrawingContextImpl.GrContext => _grContext;
 
         /// <inheritdoc />
         public void Clear(Color color)

src/Skia/Avalonia.Skia/ISkiaDrawingContextImpl.cs

@@ -6,5 +6,6 @@ namespace Avalonia.Skia
     public interface ISkiaDrawingContextImpl : IDrawingContextImpl
     {
         SKCanvas SkCanvas { get; }
+        GRContext GrContext { get; }
     }
 }