Send the available chat commands to clients which can show them

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)

src/GameLogic/Views/IChatCommandListViewPlugIn.cs

@@ -0,0 +1,20 @@
+// <copyright file="IChatCommandListViewPlugIn.cs" company="MUnique">
+// Licensed under the MIT License. See LICENSE file in the project root for full license information.
+// </copyright>
+
+namespace MUnique.OpenMU.GameLogic.Views;
+
+using MUnique.OpenMU.GameLogic.PlugIns.ChatCommands;
+
+/// <summary>
+/// Interface of a view whose client can show the available chat commands to the player.
+/// </summary>
+public interface IChatCommandListViewPlugIn : IViewPlugIn
+{
+    /// <summary>
+    /// Shows the chat commands which are available to the player, so that the client
+    /// can offer them without requiring the player to know or type any of them.
+    /// </summary>
+    /// <param name="commands">The available chat commands.</param>
+    ValueTask ShowChatCommandListAsync(IReadOnlyCollection<ChatCommandInfo> commands);
+}