This is exactly the same as the DisplayName enum in Damus iOS. Due to
the various inconsistencies in `name` and `display_name` between
clients, we have to generalize DisplayName into two variants: one name
or two names.
If we have two names, we treat it in the standard way of display_name is
the real name, and `name` is the username.
If only one is set, then it is considered both the username and "real name".
Signed-off-by: William Casarin <jb55@jb55.com>
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