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/Bus/VirtIO/RNG.h

@@ -19,7 +19,7 @@ class RNG final
     : public AtomicRefCounted<RNG>
     , public VirtIO::Device {
 public:
-    static NonnullRefPtr<RNG> must_create(PCI::DeviceIdentifier const&);
+    static NonnullLockRefPtr<RNG> must_create(PCI::DeviceIdentifier const&);
     virtual StringView purpose() const override { return class_name(); }
     virtual ~RNG() override = default;