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/Weakable.h

@@ -6,15 +6,12 @@
 
 #pragma once
 
-#ifdef KERNEL
-#    include <Kernel/Library/ThreadSafeWeakable.h>
-#else
-#    include <AK/Assertions.h>
-#    include <AK/Atomic.h>
-#    include <AK/RefCounted.h>
-#    include <AK/RefPtr.h>
-#    include <AK/StdLibExtras.h>
-#    include <sched.h>
+#include <AK/Assertions.h>
+#include <AK/Atomic.h>
+#include <AK/RefCounted.h>
+#include <AK/RefPtr.h>
+#include <AK/StdLibExtras.h>
+#include <sched.h>
 
 namespace AK {
 
@@ -125,5 +122,3 @@ private:
 }
 
 using AK::Weakable;
-
-#endif