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.

AK/WeakPtr.h

@@ -6,11 +6,7 @@
 
 #pragma once
 
-#ifdef KERNEL
-#    include <Kernel/Library/ThreadSafeWeakPtr.h>
-#else
-
-#    include <AK/Weakable.h>
+#include <AK/Weakable.h>
 
 namespace AK {
 
@@ -185,4 +181,3 @@ WeakPtr<T> make_weak_ptr_if_nonnull(T const* ptr)
 }
 
 using AK::WeakPtr;
-#endif