feat(editor): add entity operations for overworld editing

- Introduced new `entity_operations.cc` and `entity_operations.h` files to handle the insertion of entrances, exits, sprites, and items in the overworld editor.
- Updated `map_properties.cc` to include a context menu for entity insertion, allowing users to add various entities directly from the canvas.
- Enhanced `overworld_editor.cc` to manage entity insertion callbacks and streamline the editing process.

Benefits:
- Improves the functionality of the overworld editor by enabling direct manipulation of entities.
- Provides a more intuitive user experience with context-sensitive menus for entity operations.

src/app/editor/editor_library.cmake

@@ -23,6 +23,7 @@ set(
   app/editor/message/message_preview.cc
   app/editor/music/music_editor.cc
   app/editor/overworld/entity.cc
+  app/editor/overworld/entity_operations.cc
   app/editor/overworld/map_properties.cc
   app/editor/overworld/overworld_editor.cc
   app/editor/overworld/overworld_entity_renderer.cc