Merge pull request #5034 from AvaloniaUI/fixes/3281-ws-clipchildren-again

Add WS_CLIPCHILDREN to PopupImpl.

src/Windows/Avalonia.Win32/PopupImpl.cs

@@ -69,7 +69,8 @@ namespace Avalonia.Win32
         {
             UnmanagedMethods.WindowStyles style =
                 UnmanagedMethods.WindowStyles.WS_POPUP |
-                UnmanagedMethods.WindowStyles.WS_CLIPSIBLINGS;
+                UnmanagedMethods.WindowStyles.WS_CLIPSIBLINGS |
+                UnmanagedMethods.WindowStyles.WS_CLIPCHILDREN;
 
             UnmanagedMethods.WindowStyles exStyle =
                 UnmanagedMethods.WindowStyles.WS_EX_TOOLWINDOW |