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/Syscalls/unveil.cpp

@@ -79,7 +79,7 @@ ErrorOr<FlatPtr> Process::sys$unveil(Userspace<Syscall::SC_unveil_params const*>
     // However, if the user specified unveil() with "c" permissions, we don't set errno if ENOENT is encountered,
     // because they most likely intend the program to create the file for them later on.
     // If this case is encountered, the parent node of the path is returned and the custody of that inode is used instead.
-    RefPtr<Custody> parent_custody; // Parent inode in case of ENOENT
+    LockRefPtr<Custody> parent_custody; // Parent inode in case of ENOENT
     OwnPtr<KString> new_unveiled_path;
     auto custody_or_error = VirtualFileSystem::the().resolve_path_without_veil(path->view(), VirtualFileSystem::the().root_custody(), &parent_custody);
     if (!custody_or_error.is_error()) {