Hackfix for #15015. (#15676)

By default disable the `UseSaveLayerRootClip` option: this will re-enable subpixel rendering, fixing #15015 but causing #14270 to reappear.

Until the required API is added to SkiaSharp you have to choose one or the other :(

src/Avalonia.Base/Rendering/Composition/Server/ServerCompositionTarget.cs

@@ -205,8 +205,7 @@ namespace Avalonia.Rendering.Composition.Server
 
         void RenderRootToContextWithClip(IDrawingContextImpl context, ServerCompositionVisual root)
         {
-            var useLayerClip = Compositor.Options.UseSaveLayerRootClip ??
-                               Compositor.RenderInterface.GpuContext != null;
+            var useLayerClip = Compositor.Options.UseSaveLayerRootClip ?? false;
             
             using (DirtyRects.BeginDraw(context))
             {