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/IPv4Socket.h

@@ -28,7 +28,7 @@ struct PortAllocationResult {
 
 class IPv4Socket : public Socket {
 public:
-    static ErrorOr<NonnullRefPtr<Socket>> create(int type, int protocol);
+    static ErrorOr<NonnullLockRefPtr<Socket>> create(int type, int protocol);
     virtual ~IPv4Socket() override;
 
     virtual ErrorOr<void> close() override;