allow enabling of windows.ui.composition with win32 options.

src/Windows/Avalonia.Win32/Win32Platform.cs

@@ -39,6 +39,15 @@ namespace Avalonia
         public bool AllowEglInitialization { get; set; } = true;
         public bool? EnableMultitouch { get; set; }
         public bool OverlayPopups { get; set; }
+
+        /// <summary>
+        /// Render Avalonia to a Texture inside the Windows.UI.Composition tree.
+        /// </summary>
+        /// <remarks>
+        /// Supported on Windows 10 build 16299 and above. Ignored on other versions.
+        /// This is recommended if you need to use AcrylicBlur or acrylic in your applications.
+        /// </remarks>
+        public bool UseWindowsUIComposition { get; set; }
     }
 }
 

src/Windows/Avalonia.Win32/WindowImpl.cs

@@ -101,7 +101,8 @@ namespace Avalonia.Win32
             };
             _rendererLock = new ManagedDeferredRendererLock();
 
-            _isUsingComposition = Win32Platform.WindowsVersion.Major >= 10 && Win32Platform.WindowsVersion.Build >= 16299 &&
+            _isUsingComposition = Win32Platform.Options.UseWindowsUIComposition &&
+                Win32Platform.WindowsVersion.Major >= 10 && Win32Platform.WindowsVersion.Build >= 16299 &&
                     Win32GlManager.EglFeature.Display is AngleWin32EglDisplay angleDisplay &&
                     angleDisplay.PlatformApi == AngleOptions.PlatformApi.DirectX11;