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/chmod.cpp

@@ -18,7 +18,7 @@ ErrorOr<FlatPtr> Process::sys$chmod(Userspace<Syscall::SC_chmod_params const*> u
     auto params = TRY(copy_typed_from_user(user_params));
     auto path = TRY(get_syscall_path_argument(params.path));
 
-    RefPtr<Custody> base;
+    LockRefPtr<Custody> base;
     if (params.dirfd == AT_FDCWD) {
         base = current_directory();
     } else {