text: Title: Document that `output_file` listener method is called with `None` when using `--output NONE`
  Body: The `output_file` listener method is called after the output.xml file is finished. The documentation in the User Guide and in the [API docs](https://robot-framework.readthedocs.io/en/stable/autodoc/robot.api.html#robot.api.interfaces.ListenerV3.output_file) of the optional base class say that it is called with a `Path` object, but when using `--output NONE` it's actually called with `None`. This is different to the `report_file` and `log_file` methods that aren't called at all if they are disabled with `--report NONE` and `--log NONE`, respectively.
  
  We could fix this inconsistency by not calling `output_file` when using `--output NONE`. It would make the documentation consistent with the behavior and all related listener methods would also behave the same way. The change would, however, be backwards incompatible and it couldn't be done in a bug fix release. I believe it is better to keep the current behavior and just update the documentation and typing accordingly.