windows/xdg: minor cleanup of min/max size calculations

fixes #8495

src/protocols/XDGShell.hpp

@@ -99,6 +99,9 @@ class CXDGToplevelResource {
 
     bool                            good();
 
+    Vector2D                        layoutMinSize();
+    Vector2D                        layoutMaxSize();
+
     // schedule a configure event
     uint32_t setSize(const Vector2D& size);
     uint32_t setMaximized(bool maximized);