User mentions and handles show a grey dot to indicate that a user is disabled or unreachable. Currently, "unreachable" means something like "email address is unverified, and auth.require-email-verification is enabled".

However, after T12237, these users aren't reachable even if auth.require-email-verification is off. We should show a grey dot in this case (indicating "this user isn't getting notified").

We should also make the meaning of the dot more clear, likely by using some of the approaches discussed in T12157 for "Disabled".