Fix/win32 no border sysmenu (#19923)

* remove ws_sysmenu from non full decoration windows

* update decorated window sample to not resize on maximize

samples/ControlCatalog/DecoratedWindow.xaml.cs

@@ -19,7 +19,8 @@ namespace ControlCatalog
             ctl.Cursor = new Cursor(cursor);
             ctl.PointerPressed += (i, e) =>
             {
-                BeginResizeDrag(edge, e);
+                if (WindowState == WindowState.Normal)
+                    BeginResizeDrag(edge, e);
             };
         }
 

src/Windows/Avalonia.Win32/WindowImpl.cs

@@ -1484,7 +1484,7 @@ namespace Avalonia.Win32
                 else
                     style &= ~WindowStyles.WS_MAXIMIZEBOX;
 
-                const WindowStyles fullDecorationFlags = WindowStyles.WS_CAPTION | WindowStyles.WS_BORDER;
+                const WindowStyles fullDecorationFlags = WindowStyles.WS_CAPTION | WindowStyles.WS_BORDER | WindowStyles.WS_SYSMENU;
 
                 if (newProperties.Decorations == SystemDecorations.Full)
                 {