Kernel: Move Lockable into its own header

Kernel/Locking/Lockable.h

@@ -0,0 +1,35 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <Kernel/Locking/Mutex.h>
+
+namespace Kernel {
+
+template<typename T>
+class Lockable {
+public:
+    Lockable() = default;
+    Lockable(T&& resource)
+        : m_resource(move(resource))
+    {
+    }
+    [[nodiscard]] Mutex& lock() { return m_lock; }
+    [[nodiscard]] T& resource() { return m_resource; }
+
+    [[nodiscard]] T lock_and_copy()
+    {
+        MutexLocker locker(m_lock);
+        return m_resource;
+    }
+
+private:
+    T m_resource;
+    Mutex m_lock;
+};
+
+}