feat(editor): integrate session management into EditorManager

- Added a new `session_types` module to encapsulate session-related structures and logic, including `EditorSet` and `RomSession`.
- Refactored `EditorManager` to utilize `SessionCoordinator` for session management, enhancing modularity and clarity.
- Updated various methods to replace direct references to current ROM and editor sets with calls to `SessionCoordinator`, improving session handling.
- Removed redundant session management logic from `EditorManager`, delegating responsibilities to `SessionCoordinator`.

Benefits:
- Streamlines session management, making it easier to handle multiple sessions and their associated editors.
- Enhances code maintainability by centralizing session-related logic and reducing coupling within the `EditorManager`.
- Improves overall architecture by promoting a clearer separation of concerns between session management and editor functionality.

src/app/editor/editor_library.cmake

@@ -14,6 +14,7 @@ set(
   app/editor/dungeon/dungeon_usage_tracker.cc
   app/editor/dungeon/object_editor_card.cc
   app/editor/editor_manager.cc
+  app/editor/session_types.cc
   app/editor/graphics/gfx_group_editor.cc
   app/editor/graphics/graphics_editor.cc
   app/editor/graphics/screen_editor.cc