To prevent new contributors who are adding new user settings from
being confused about the legacy dicts for display settings and
notifications settings, we create `modern_settings` and
`modern_notifications_settings` dicts with comments documenting
that new user settings should be added to one of them.
Note that the `modern_notification_settings` is a placeholder for
new notifications settings as there have been no new notification
settings added since 430c5cb8 (when the legacy dicts were created)
and is currently annotated as `Dict[str, Any]` (which can be
removed if/when a new setting is added).
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