Fixes#22984
Add an `@` icon in unread topics where user is mentioned.
We track a new set of `stream_id:topic` pairs for the unread mentions
so that recent topics instantly knows if a topic is unread and mentioned
or not.
This commit adds private messages to the Recent topics view, to make
it an all-encompassing overview of recent activity visible to the user.
We add a filter "Include PM" to toggle whether PMs should be shown in
recent topics.
Fixes#19449.
Since we don't process private messages yet, we don't
need to re-render when we receive a new private message
as it doesn't change any data related to recent_topics.
This data structure has never been one that we actually render into
the DOM; instead, its role is to support clicking into view that
contain muted streams and topics quickly.
This downgrade makes that situation much more explicit, and is also
useful refactoring to help simpify the upcoming changes in #16746.
Signed-off-by: Anders Kaseorg <anders@zulip.com>
