Show pronouns in @-mention autocomplete

[gnprice]

There's an upcoming feature in Zulip web which we should match: zulip/zulip#26924

As proposed on CZO, we should show pronouns in @-mention typeahead. […]

Details:

• Nothing will be shown if the user doesn't have a non-empty pronoun-type custom profile field.
• If the user does have such a field, we can put pronouns in ( ) after status emoji but before the user's email (if present).
• If there are multiple pronoun fields in the organization, we should use whichever one is earlier in the list of custom profile fields. No pronoun should be shown if that field is empty.

[…]

CZO thread

The zulip/zulip issue also says:

We can also show [pronouns] in the addressee typeahead for DMs.

In zulip-flutter, we don't yet have a UI that corresponds to that: that's #127. So if we haven't yet done #127 when we take up this issue, then we'll leave that part out of scope, and we'll make it part of #127 instead.