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/SysFS/Subsystems/DeviceIdentifiers/Directory.h

@@ -14,7 +14,7 @@ namespace Kernel {
 class SysFSDeviceIdentifiersDirectory final : public SysFSDirectory {
 public:
     virtual StringView name() const override { return "dev"sv; }
-    static NonnullRefPtr<SysFSDeviceIdentifiersDirectory> must_create(SysFSRootDirectory const&);
+    static NonnullLockRefPtr<SysFSDeviceIdentifiersDirectory> must_create(SysFSRootDirectory const&);
 
     static SysFSDeviceIdentifiersDirectory& the();