Use composition instead of classes with Layout and LifeCycleHook

[rmorshea]

This is similar to #324 but specifically focused on the Layout and LifeCycleHook since those will be the most complex to refactor. I'm not really sure what the interface would ultimately look like - whether there would still be a layout with render and dispatch methods, or if those would be functions accepting some sort of LayoutState instead. Maybe a bit like:

with layout_context(component) as layout:
    old_state, new_state = await render(layout)
    diff = compute_diff(old_state, new_state)
    await dispatch_event(layout)

You could take a similar approach to hooks as well, but just applying functions to objects containing state.

[rmorshea]

This is complete. The drastic changes suggested in the original comment aren't really productive because there's not much use in having access to the internal state of Layout. The ability to substitute Layout for some other implementation is what is most useful.