implement GetScaleFactor for GLWindow.

src/Avalonia.Windowing/Bindings/GlWindow.cs

@@ -25,6 +25,9 @@ namespace Avalonia.Windowing.Bindings
         [DllImport("winit_wrapper")]
         private static extern LogicalSize winit_gl_window_get_size(IntPtr handle);
 
+        [DllImport("winit_wrapper")]
+        private static extern double winit_gl_window_get_dpi_scale_factor(IntPtr handle);
+
         [DllImport("winit_wrapper")]
         private static extern LogicalPosition winit_gl_window_get_position(IntPtr handle);
 
@@ -89,6 +92,11 @@ namespace Avalonia.Windowing.Bindings
             return (size.Width, size.Height);
         }
 
+        public double GetScaleFactor ()
+        {
+            return winit_gl_window_get_dpi_scale_factor(_handle);
+        }
+
         public (double, double) GetFramebufferSize()
         {
             return GetSize();

src/Avalonia.Windowing/Bindings/IWindowWrapper.cs

@@ -12,6 +12,7 @@ namespace Avalonia.Windowing.Bindings
         void SetTitle(string title);
         void SetSize(double width, double height);
 
+        double GetScaleFactor();
         (double, double) GetSize();
         (double, double) GetPosition();
 

src/Avalonia.Windowing/WIndowingPlatform.cs

@@ -10,12 +10,6 @@ using Avalonia.Windowing.Bindings;
 
 namespace Avalonia.Windowing
 {
-    public class PlatformSettings : IPlatformSettings
-    {
-        public Size DoubleClickSize => new Size(4, 4);
-        public TimeSpan DoubleClickTime => TimeSpan.FromMilliseconds(200);
-    }
-
     public class DummyPlatformHandle : IPlatformHandle
     {
         public IntPtr Handle => IntPtr.Zero;

src/Avalonia.Windowing/WindowImpl.cs

@@ -55,7 +55,7 @@ namespace Avalonia.Windowing
             }
         }
 
-        public double Scaling => 192 / 96;
+        public double Scaling => _windowWrapper.GetScaleFactor();
 
         public IEnumerable<object> Surfaces => new List<object>() { _windowWrapper };