LibJS/Bytecode: Add Bytecode::Operand

An Operand is either a register, a local, or a constant (index into the
executable's constant table)

Userland/Libraries/LibJS/Bytecode/Operand.h

@@ -0,0 +1,44 @@
+/*
+ * Copyright (c) 2024, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Types.h>
+#include <LibJS/Forward.h>
+
+namespace JS::Bytecode {
+
+class Operand {
+public:
+    enum class Type {
+        Register,
+        Local,
+        Constant,
+    };
+
+    [[nodiscard]] bool operator==(Operand const&) const = default;
+
+    explicit Operand(Type type, u32 index)
+        : m_type(type)
+        , m_index(index)
+    {
+    }
+
+    explicit Operand(Register);
+
+    [[nodiscard]] bool is_register() const { return m_type == Type::Register; }
+    [[nodiscard]] bool is_local() const { return m_type == Type::Local; }
+    [[nodiscard]] bool is_constant() const { return m_type == Type::Constant; }
+
+    [[nodiscard]] Type type() const { return m_type; }
+    [[nodiscard]] u32 index() const { return m_index; }
+
+private:
+    Type m_type {};
+    u32 m_index { 0 };
+};
+
+}