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/Devices/MemoryDevice.h

@@ -16,7 +16,7 @@ class MemoryDevice final : public CharacterDevice {
     friend class DeviceManagement;
 
 public:
-    static NonnullRefPtr<MemoryDevice> must_create();
+    static NonnullLockRefPtr<MemoryDevice> must_create();
     ~MemoryDevice();
 
     virtual ErrorOr<Memory::Region*> mmap(Process&, OpenFileDescription&, Memory::VirtualRange const&, u64 offset, int prot, bool shared) override;