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/KCOVInstance.h

@@ -53,7 +53,7 @@ private:
     u64 m_buffer_size_in_entries { 0 };
     size_t m_buffer_size_in_bytes { 0 };
     kcov_pc_t* m_buffer { nullptr };
-    RefPtr<Memory::AnonymousVMObject> m_vmobject;
+    LockRefPtr<Memory::AnonymousVMObject> m_vmobject;
 
     // Here to ensure it's not garbage collected at the end of open()
     OwnPtr<Memory::Region> m_kernel_region;