Kernel: Implement contended, ref-counted resource framework

This is some syntaxic sugar to use a ContendedResource object with
reference counting. This effectively dissociates merely holding a
reference to an object and actually using the object in a way that
requires locking it against concurrent use.

Kernel/Locking/NonnullRefContendedPtrVector.h

@@ -0,0 +1,17 @@
+/*
+ * Copyright (c) 2021, the SerenityOS developers.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/NonnullPtrVector.h>
+#include <Kernel/Locking/NonnullRefContendedPtr.h>
+
+namespace Kernel {
+
+template<typename T, size_t inline_capacity = 0>
+using NonnullRefContendedPtrVector = AK::NonnullPtrVector<NonnullRefContendedPtr<T>, inline_capacity>;
+
+}