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/FileSystem/SysFS/Registry.h

@@ -31,7 +31,7 @@ public:
     SysFSBusDirectory& buses_directory();
 
 private:
-    NonnullRefPtr<SysFSRootDirectory> m_root_directory;
+    NonnullLockRefPtr<SysFSRootDirectory> m_root_directory;
     Spinlock m_root_directory_lock { LockRank::None };
 };