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/utimensat.cpp

@@ -40,8 +40,8 @@ ErrorOr<FlatPtr> Process::sys$utimensat(Userspace<Syscall::SC_utimensat_params c
     }
 
     OwnPtr<KString> path;
-    RefPtr<OpenFileDescription> description;
-    RefPtr<Custody> base;
+    LockRefPtr<OpenFileDescription> description;
+    LockRefPtr<Custody> base;
 
     auto path_or_error = get_syscall_path_argument(params.path);
     if (path_or_error.is_error()) {