Revert "WindowServer: Remove redundant Window::set_visible()..."

This reverts commit 239520ae54.

The call to set_visible() is not redundant. Removing the call leads
to the "start" button in the taskbar not being painted as "pressed" even
when it is.

Userland/Services/WindowServer/Menu.cpp

@@ -638,6 +638,7 @@ void Menu::do_popup(const Gfx::IntPoint& position, bool make_input, bool as_subm
     }
 
     window.move_to(adjusted_pos);
+    set_visible(true);
     MenuManager::the().open_menu(*this, make_input);
     WindowManager::the().did_popup_a_menu({});
 }