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/read.cpp

@@ -13,7 +13,7 @@ namespace Kernel {
 
 using BlockFlags = Thread::FileBlocker::BlockFlags;
 
-static ErrorOr<NonnullRefPtr<OpenFileDescription>> open_readable_file_description(auto& fds, int fd)
+static ErrorOr<NonnullLockRefPtr<OpenFileDescription>> open_readable_file_description(auto& fds, int fd)
 {
     auto description = TRY(fds.with_shared([&](auto& fds) { return fds.open_file_description(fd); }));
     if (!description->is_readable())