Create extended user mention syntax when needed.

[aero31aero]

Recently, in zulip/zulip#10243 we merged support for the following mention syntax to zulip/zulip:

@**Full Name|1234(id)**

This is to allow us to mention users with the same full name, and is optional. The web app intelligently adds the new syntax only when the users have the same full name, and uses the simpler syntax for others.

Example: https://chat.zulip.org/#narrow/stream/7-test-here/topic/user.20mention

We should:

1. Add support for this syntax in the terminal client.
2. Ensure that it is behind a feature flag because it would break mentions in older servers/any non CZO server for now.

[timabbott]

We can do a check against the server version being 1.9.0 or greater, for this.

[neiljp]

I started to look into this and it seems that ZT uses the rendered text provided by the app to understand mentions from the server - the linked example renders OK as-is? So not the same issue as in the python lib.

If the change is indeed primarily regarding sending to capable servers, this only currently appears relevant to using '@' to reply with a quote? (though it would be useful to support 'x' - compose message - from the users search bar too)

[zee-bit]

@neiljp This issue seems to be fixed by #854, should we close this?

[neiljp]

This is now likely pending on #928.

[zee-bit]

Ahh...sorry. It was user mention syntax and not the quoting syntax we recently merged. :)