stream_edit: Extract update_muting_rendering.
stream_edit: Extract update_muting_rendering.

rht/zulip,zulip/zulip,rht/zulip,andersk/zulip,kou/zulip,rht/zulip,andersk/zulip,andersk/zulip,kou/zulip,rht/zulip,rht/zulip,andersk/zulip,zulip/zulip,kou/zulip,andersk/zulip,zulip/zulip,andersk/zulip,kou/zulip,andersk/zulip,kou/zulip,rht/zulip,zulip/zulip,zulip/zulip,zulip/zulip,kou/zulip,kou/zulip,rht/zulip,zulip/zulip