Provide Span overload for SetRectRadii (#2949)

binding/SkiaSharp/SKRoundRect.cs

@@ -122,6 +122,12 @@ namespace SkiaSharp
 		{
 			if (radii == null)
 				throw new ArgumentNullException (nameof (radii));
+
+			SetRectRadii(rect, radii.AsSpan());
+		}
+
+		public void SetRectRadii (SKRect rect, ReadOnlySpan<SKPoint> radii)
+		{
 			if (radii.Length != 4)
 				throw new ArgumentException ("Radii must have a length of 4.", nameof (radii));