Adds the server side of the chat command list: a view plugin which
sends one ChatCommandInfo per available command, and the handler for
the request of a client which supports it.
Both are limited to the extended protocol, so classic clients don't
receive messages they can't understand. The commands come from
GetAvailableChatCommandInfos, so a player only learns about the ones
he may execute, and deactivated ones stay out.
Executing a command needs nothing new: the client sends the composed
command line as an ordinary chat message, which the chat message
processor already routes to the command without broadcasting it.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MSpK6jkyF8ZS5nYXyGwYxA
(cherry picked from commit f3a9cb132c295863942bb0f06f40cde231e57907)
