Generate topic links as permalinks, using /with/

[gnprice]

This is part of the upcoming Zulip feature zulip/zulip#21505 , and a followup to #5866.

Since #5866, mobile understands the new topic permalink URLs. Once the web app does too (PR zulip/zulip#30114), we should start generating them, conditioned on that Zulip feature level. This is the mobile counterpart to PR zulip/zulip#30644 .

Specifically, in the topic action sheet we have an option "Copy link to topic". That option should start producing topic permalinks, just like the similar option in web's left sidebar will do with zulip/zulip#30644 .

[chrisbobbe]

Looks like we're still waiting for zulip/zulip#30114; when that's merged, we'll know what feature level to use. (Earlier today I mistakenly thought this was ripe to work on.)

[alya]

ETA on server: August 2024