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/Syscalls/stat.cpp

@@ -4,9 +4,9 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
-#include <AK/NonnullRefPtrVector.h>
 #include <Kernel/FileSystem/Custody.h>
 #include <Kernel/FileSystem/VirtualFileSystem.h>
+#include <Kernel/Library/NonnullLockRefPtrVector.h>
 #include <Kernel/Process.h>
 
 namespace Kernel {
@@ -29,7 +29,7 @@ ErrorOr<FlatPtr> Process::sys$stat(Userspace<Syscall::SC_stat_params const*> use
 
     auto path = TRY(get_syscall_path_argument(params.path));
 
-    RefPtr<Custody> base;
+    LockRefPtr<Custody> base;
     if (params.dirfd == AT_FDCWD) {
         base = current_directory();
     } else {