Rewrite commands

Signed-off-by: Jaida Wu <mlgmxyysd@meowcat.org>

src/main/java/emu/grasscutter/command/CommandHandler.java

@@ -0,0 +1,25 @@
+package emu.grasscutter.command;
+
+import emu.grasscutter.Grasscutter;
+import emu.grasscutter.game.GenshinPlayer;
+
+import java.util.List;
+
+public interface CommandHandler {
+    /**
+     * Send a message to the target.
+     *
+     * @param player  The player to send the message to, or null for the server console.
+     * @param message The message to send.
+     */
+    static void sendMessage(GenshinPlayer player, String message) {
+        if (player == null) {
+            Grasscutter.getLogger().info(message);
+        } else {
+            player.dropMessage(message);
+        }
+    }
+
+    default void onCommand(GenshinPlayer sender, List<String> args) {
+    }
+}