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/FileSystem.cpp

@@ -53,7 +53,7 @@ void FileSystem::sync()
 {
     Inode::sync_all();
 
-    NonnullRefPtrVector<FileSystem, 32> file_systems;
+    NonnullLockRefPtrVector<FileSystem, 32> file_systems;
     {
         InterruptDisabler disabler;
         for (auto& it : all_file_systems())