Constrain CenterOwner window to screen. (AvaloniaUI#14982)

* Constrain CenterOwner window to screen.

This logic is also present in WPF: https://github.com/dotnet/wpf/blob/3880169c020787b7e3383acb3679e5e4d538c602/src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Window.cs#L3707-L3711

Fixes AvaloniaUI#2578

* Ensure min <= max when constraining window pos.

src/Avalonia.Controls/Window.cs

@@ -11,6 +11,7 @@
 using Avalonia.Platform;
 using Avalonia.Reactive;
 using Avalonia.Styling;
+using Avalonia.Utilities;
 
 namespace Avalonia.Controls
 {
@@ -943,7 +944,20 @@ private void SetWindowStartupLocation(Window? owner = null)
                 var ownerRect = new PixelRect(
                     owner.Position,
                     PixelSize.FromSize(ownerSize, scaling));
-                Position = ownerRect.CenterRect(rect).Position;
+                var childRect = ownerRect.CenterRect(rect);
+
+                if (Screens.ScreenFromWindow(this)?.WorkingArea is { } constraint)
+                {
+                    var maxX = constraint.Right - rect.Width;
+                    var maxY = constraint.Bottom - rect.Height;
+
+                    if (constraint.X <= maxX)
+                        childRect = childRect.WithX(MathUtilities.Clamp(childRect.X, constraint.X, maxX));
+                    if (constraint.Y <= maxY)
+                        childRect = childRect.WithY(MathUtilities.Clamp(childRect.Y, constraint.Y, maxY));
+                }
+
+                Position = childRect.Position;
             }
         }