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/File.cpp

@@ -15,7 +15,7 @@ namespace Kernel {
 File::File() = default;
 File::~File() = default;
 
-ErrorOr<NonnullRefPtr<OpenFileDescription>> File::open(int options)
+ErrorOr<NonnullLockRefPtr<OpenFileDescription>> File::open(int options)
 {
     auto description = OpenFileDescription::try_create(*this);
     if (!description.is_error()) {