refactor: Remove OverworldEditorManager and GraphicsManager for Simplification

- Deleted OverworldEditorManager and OverworldGraphicsManager classes to streamline the codebase and reduce complexity in the overworld editor.
- Updated CMake configuration to remove references to the deleted files, ensuring a clean build environment.
- Adjusted OverworldEditor to handle graphics management directly, improving maintainability and reducing the number of dependencies.
- Enhanced the initialization and update methods in OverworldEditor to accommodate the removal of the manager classes, ensuring continued functionality.
- Cleaned up related header files to reflect the removal of obsolete classes and methods, enhancing clarity and organization.

src/app/editor/editor_library.cmake

@@ -18,7 +18,6 @@ set(
   app/editor/dungeon/dungeon_room_loader.cc
   app/editor/dungeon/dungeon_usage_tracker.cc
   app/editor/overworld/overworld_editor.cc
-  app/editor/overworld/overworld_editor_manager.cc
   app/editor/overworld/scratch_space.cc
   app/editor/sprite/sprite_editor.cc
   app/editor/music/music_editor.cc
@@ -36,7 +35,6 @@ set(
   app/editor/graphics/gfx_group_editor.cc
   app/editor/overworld/entity.cc
   app/editor/overworld/overworld_entity_renderer.cc
-  app/editor/overworld/overworld_graphics_manager.cc
   app/editor/system/settings_editor.cc
   app/editor/system/command_manager.cc
   app/editor/system/extension_manager.cc