LVN command - add_class, remove_class, and toggle_class

[js client implementation](https://github.com/phoenixframework/phoenix_live_view/blob/main/assets/js/phoenix_live_view/js.js#L257-L291)

Example data:

```elixir
[
  ["add_class", %{names: ["show"]}]
]
```

[Docs](https://hexdocs.pm/phoenix_live_view/Phoenix.LiveView.JS.html#add_class/1)