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/WorkQueue.cpp

@@ -23,7 +23,7 @@ UNMAP_AFTER_INIT void WorkQueue::initialize()
 
 UNMAP_AFTER_INIT WorkQueue::WorkQueue(StringView name)
 {
-    RefPtr<Thread> thread;
+    LockRefPtr<Thread> thread;
     auto name_kstring = KString::try_create(name);
     if (name_kstring.is_error())
         TODO();