Improve message formatting to clients

Replaces tab indents with an extra linebreak.
Also adds / to the start of command usage.
Neither of these changes affect messages to the server console log.

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

@@ -28,7 +28,7 @@ public interface CommandHandler {
         if (player == null) {
             Grasscutter.getLogger().info(event.getMessage());
         } else {
-            player.dropMessage(event.getMessage());
+            player.dropMessage(event.getMessage().replace("\n\t", "\n\n"));
         }
     }
 
@@ -44,6 +44,9 @@ public interface CommandHandler {
             if (alias.length() < command.length())
                 command = alias;
         }
+        if (player != null) {
+            command = "/" + command;
+        }
         String target = switch (annotation.targetRequirement()) {
             case NONE -> "";
             case OFFLINE -> "@<UID> ";  // TODO: make translation keys for offline and online players