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/FileBackedFileSystem.h

@@ -26,7 +26,7 @@ protected:
 private:
     virtual bool is_file_backed() const override { return true; }
 
-    mutable NonnullRefPtr<OpenFileDescription> m_file_description;
+    mutable NonnullLockRefPtr<OpenFileDescription> m_file_description;
 };
 
 }