LibChess: Add the UCI quit command

Author: https://github.com/tcl3
Commit: 13dbc69c23
Pull-request: https://github.com/SerenityOS/serenity/pull/18140
Issue: https://github.com/SerenityOS/serenity/issues/17427
Reviewed-by: https://github.com/LucasChollet
Reviewed-by: https://github.com/petelliott

Userland/Libraries/LibChess/UCICommand.h

@@ -268,4 +268,16 @@ public:
     // FIXME: Add additional fields.
 };
 
+class QuitCommand : public Command {
+public:
+    explicit QuitCommand()
+        : Command(Command::Type::Quit)
+    {
+    }
+
+    static QuitCommand from_string(StringView command);
+
+    virtual DeprecatedString to_deprecated_string() const override;
+};
+
 }