enhancement
During layout configuration #24085, it was noticed that a new tab cannot be created in the main window if an external window is open, because two different ContentHandlers are registered for the same ID.
If you want to open an external window, a new WindowComponent is instantiated using the WindowManager. The parent of the WindowComponent is set to the WindowManager’s holder and is thus added to the component tree.
Instead, the new `WindowComponent` should be registered with the `MainLayout` of the `Opener` component.
Test
No test.