Copy link to message

[gnprice]

We should make it easy to get a link to a particular message you're looking at.

This is particularly useful for pointing to the message in a message you send in a different conversation, or in something you write in some other system outside of Zulip.

In the legacy zulip-mobile app we don't have this, and instead have a "Share" option that isn't super useful. We've talked there occasionally for years about replacing it with "copy link":

• Replace "Share" with "Copy link to message" zulip-mobile#2623

but never quite put it on the agenda to actually do. Here we should just do it.

For an example for the UI and copying to the clipboard, see the existing "Copy message text" item in the message action sheet. For constructing the URL for the message, see the implementation of quote-and-reply.