Kernel: Make self-contained locking smart pointers their own classes

Until now, our kernel has reimplemented a number of AK classes to
provide automatic internal locking:

- RefPtr
- NonnullRefPtr
- WeakPtr
- Weakable

This patch renames the Kernel classes so that they can coexist with
the original AK classes:

- RefPtr => LockRefPtr
- NonnullRefPtr => NonnullLockRefPtr
- WeakPtr => LockWeakPtr
- Weakable => LockWeakable

The goal here is to eventually get rid of the Lock* classes in favor of
using external locking.

Kernel/Tasks/FinalizerTask.cpp

@@ -28,7 +28,7 @@ static void finalizer_task(void*)
 
 UNMAP_AFTER_INIT void FinalizerTask::spawn()
 {
-    RefPtr<Thread> finalizer_thread;
+    LockRefPtr<Thread> finalizer_thread;
     auto finalizer_process = Process::create_kernel_process(finalizer_thread, KString::must_create(finalizer_task_name), finalizer_task, nullptr);
     VERIFY(finalizer_process);
     g_finalizer = finalizer_thread;