Merge pull request #8365 from ltetak/feature/borders_different_dpis

OffScreenMargin calculation with different DPI monitors calculation

src/Windows/Avalonia.Win32/WindowImpl.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.ComponentModel;
+using System.Linq;
 using System.Runtime.InteropServices;
 using Avalonia.Controls;
 using Avalonia.Automation.Peers;
@@ -208,6 +209,8 @@ namespace Avalonia.Win32
             }
         }
 
+        private double PrimaryScreenRenderScaling => Screen.AllScreens.FirstOrDefault(screen => screen.Primary)?.PixelDensity ?? 1;
+
         public double RenderScaling => _scaling;
 
         public double DesktopScaling => RenderScaling;
@@ -944,7 +947,7 @@ namespace Avalonia.Win32
             if (WindowState == WindowState.Maximized)
             {
                 _extendedMargins = new Thickness(0, (borderCaptionThickness.top - borderThickness.top) / RenderScaling, 0, 0);
-                _offScreenMargin = new Thickness(borderThickness.left / RenderScaling, borderThickness.top / RenderScaling, borderThickness.right / RenderScaling, borderThickness.bottom / RenderScaling);
+                _offScreenMargin = new Thickness(borderThickness.left / PrimaryScreenRenderScaling, borderThickness.top / PrimaryScreenRenderScaling, borderThickness.right / PrimaryScreenRenderScaling, borderThickness.bottom / PrimaryScreenRenderScaling);
             }
             else
             {