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/Net/LoopbackAdapter.h

@@ -15,7 +15,7 @@ private:
     LoopbackAdapter(NonnullOwnPtr<KString>);
 
 public:
-    static RefPtr<LoopbackAdapter> try_create();
+    static LockRefPtr<LoopbackAdapter> try_create();
     virtual ~LoopbackAdapter() override;
 
     virtual void send_raw(ReadonlyBytes) override;