Rationale:
1. A much more experienced developer, whom I highly respect, suggested to empty VimStateMachineImpl constructor in his TODO comment.
2. I aim for VimStateMachine to be a data class rather than being a container for both data and complex logic.
3. From an architectural perspective, it is more correct. Editors do have state (or they may possess a single global state if the corresponding option is set), but a state does not own an editor.
