Typing dots: none for commands and private messages, and no flood of stop notices

A line that starts with "/" is a command, a whisper or party chat, so typing
one no longer shows dots to the whole server. Dots already showing are cleared
when the line becomes one.

A "stopped typing" notice was relayed every time it arrived, while "typing"
was held to one per 200 ms, so a modified client could flood everyone through
the host. A lobby's host and a dedicated server now pass a stop on only when
that player's dots are up, which is at most once per accepted "typing".

Server/server_host.cpp

@@ -1267,12 +1267,17 @@ void Host::receive(std::uint64_t peer, std::span<const std::uint8_t> bytes, std:
         return;
     }
     // Grey dots above the sender. Not a chat line, and not logged. A player who may not
-    // chat sends none. "On" is held to a few a second; "off" always goes through.
+    // chat sends none. "On" is held to a few a second, and "off" is passed on only after an
+    // "on", so neither can flood the relay.
     if (p.kind == PacketKind::typing) {
         if (!routed_source(p, link->member, peer, true, id_) || !may(peer, multiplayer::role_chat)) return;
         if (p.typing) {
             if (link->typing_notice && now_ < link->typing_notice + 200000) return;
             link->typing_notice = now_;
+            link->typing = true;
+        } else {
+            if (!link->typing) return;
+            link->typing = false;
         }
         link->last_packet = now_;
         active(*link);