Optimize SKRoundRectCache Clear Method for .NET 6+ (#17605)

This changes optimizes the `Clear` method in `SKRoundRectCache`. For .NET 6 and higher versions, a faster clearing technique is utilized, enhancing performance.

src/Skia/Avalonia.Skia/SKRoundRectCache.cs

@@ -91,9 +91,13 @@ namespace Avalonia.Skia
             base.Clear();
 
             // Clear out the cache of SKPoint arrays.
+#if NET6_0_OR_GREATER
+            _radiiCache.Clear();
+#else
             while (_radiiCache.TryTake(out var item))
             {
             }
+#endif
         }
     }
 }