message_edit: Return a bool in maybe_send_resolve_topic_notifications.
message_edit: Return a bool in maybe_send_resolve_topic_notifications.

Whether we sent a resolve topic notification or not may be useful in
the caller. It was originally intended to be used in #21712, but may
only be relevant for future logging.

Part of #21712.

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