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/poll.cpp

@@ -50,7 +50,7 @@ ErrorOr<FlatPtr> Process::sys$poll(Userspace<Syscall::SC_poll_params const*> use
     TRY(m_fds.with_shared([&](auto& fds) -> ErrorOr<void> {
         for (size_t i = 0; i < params.nfds; i++) {
             auto& pfd = fds_copy[i];
-            RefPtr<OpenFileDescription> description;
+            LockRefPtr<OpenFileDescription> description;
             auto description_or_error = fds.open_file_description(pfd.fd);
             if (!description_or_error.is_error())
                 description = description_or_error.release_value();