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/FileSystem/FileSystem.h

@@ -8,10 +8,10 @@
 
 #include <AK/AtomicRefCounted.h>
 #include <AK/Error.h>
-#include <AK/RefPtr.h>
 #include <AK/StringView.h>
 #include <Kernel/FileSystem/InodeIdentifier.h>
 #include <Kernel/Forward.h>
+#include <Kernel/Library/LockRefPtr.h>
 #include <Kernel/Locking/Mutex.h>
 #include <Kernel/UnixTypes.h>
 #include <Kernel/UserOrKernelBuffer.h>