Kernel: Move Lockable into its own header

Kernel/Locking/Mutex.h

@@ -182,28 +182,6 @@ private:
     bool m_locked { true };
 };
 
-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;
-};
-
 class ScopedLockRelease {
     AK_MAKE_NONCOPYABLE(ScopedLockRelease);