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/Devices/Graphics/Directory.h

@@ -17,7 +17,7 @@ class SysFSGraphicsDirectory : public SysFSDirectory {
 
 public:
     virtual StringView name() const override { return "graphics"sv; }
-    static NonnullRefPtr<SysFSGraphicsDirectory> must_create(SysFSDevicesDirectory const&);
+    static NonnullLockRefPtr<SysFSGraphicsDirectory> must_create(SysFSDevicesDirectory const&);
 
 private:
     explicit SysFSGraphicsDirectory(SysFSDevicesDirectory const&);