refactor(editor): remove MenuManager class and its associated files

- Deleted the MenuManager class implementation and header files from the project.
- Updated CMake configuration to reflect the removal of MenuManager, simplifying the editor's UI management.

Benefits:
- Reduced code complexity by eliminating unused components.
- Improved maintainability of the editor's UI structure.

src/app/editor/editor_library.cmake

@@ -47,7 +47,6 @@ set(
   app/editor/ui/background_renderer.cc
   app/editor/ui/editor_selection_dialog.cc
   app/editor/ui/menu_builder.cc
-  app/editor/ui/menu_manager.cc
   app/editor/ui/welcome_screen.cc
   app/editor/ui/workspace_manager.cc
 )