Apply reverse linkifiers on paste

[gnprice]

I.e., this Zulip feature:

You can configure linkifiers to work in reverse as well: when you paste a URL that matches the linkifier into the compose box, Zulip will automatically convert it to linked text (e.g., https://github.com/zulip/zulip/issues/2468 becomes #2468).

(from https://zulip.com/help/add-a-custom-linkifier )

That behavior was recently added in Zulip web. We should do the same in the mobile app.

[izohaib]

I would like to work on this issue. Could you please assign it to me?

[izohaib]

Hello @gnprice, I noticed the server is sending reverse_template as null for most linkifiers, and for the zulip-flutter linkifier it returns #F123 instead of the expected #F{id}

[gnprice]

If you have a question about the server's behavior, a Zulip chat thread is a much better venue for discussion than GitHub. The #mobile-dev-help channel is a good place to start.