Add suport for emojis in streams/topics titles

[Igorgro]

I want to suggest adding support for emojis (including custom server emojis) in stream and topic titles using their codes, like :calendar:

[cshemtov]

@zulipbot claim

[zulipbot]

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[alya]

#10611 suggested doing this for user names as well.

[zulipbot]

Hello @zulip/server-emoji members, this issue was labeled with the "area: emoji" label, so you may want to check it out!