Let Plugin Windows Be Maximized on X11 (#16335)

wxGTK types every wxDialog as a dialog window, and Mutter offers no
maximize for anything but a normal window, so the maximize button and
shortcut did nothing on GNOME under X11. Modeless plugin windows are now
normal windows, kept off the taskbar as before. Modal ones stay dialogs
so the window manager keeps routing focus from the main window to them.

src/slic3r/plugin/host/PluginHostUi.cpp

@@ -399,6 +399,7 @@ py::object ui_create_window(const std::string& html, const std::string& title, i
             if (UiRegistry::instance().is_open(new_id))
                 dlg->Destroy();
         } else {
+            dlg->use_normal_window_type();
             dlg->Show();
         }
     });