Earlier, a user can only mute a topic from its recipient bar but can't
unmute it from there (and in fact we displayed an option to mute even
if the topic was already muted!). This commit fixes that bug and
allows a user also to unmute the topic from its recipient bar.
There are two core issues here;
* We did not have code, an icon, etc. for the "already muted" case in
the recipient bar logic at all.
* We did not rerender messages in !excludes_muted_topics views when
muting state changed.
See: 660475bd0c for background on when
we started only rerendering the streams with excludes_muted_topics
after muting changes. Rerendering of newly muted topics are important
for live rendering if a user is narrowed to that topic itself, which
are essentially all excludes_muted_topics narrows anyway.
Hence, now, we rerender by calling the `rerender` function for muted
topics (which is done just before we update the items for muting via
the function: `update_items_for_topic_muting`).
Tweaked by tabbott to add comments explaining the reasoning and
long-term plans.
Fixes#15223.
bf41f455cd