live: Implement config propagation utils

[s0]

One of the biggest parts of work to componentise existing code, or to create new components, is to link together all the config updating and propagation up & down, and respond to config change events, and pass that down to each of the individual child components.

This process could be simplified if we introduced a modular way of propagating configurations, and linking sub-configurations. We could also simplify the handling of more specific types at type boundaries (such as plugin config / input config) by doing the type checking in a single place, and just linking using unknown to reduce the need for type coercion.

It would need to:

• accept applyConfig and

• allow for adding children, example:

  const childConfig = c.addChild(
    // Get current value
    current => current.children[id],
    // Update current value
    (current, update) => ({
      ...current,
      children: {
        ...current.children,
        [id]: update(current.children[id])
      }),
    // Optional: delete current child (required for `.delete()`
    (current) => {
      const children = {...current.children};
      delete children[id];
      return { ...current, children};
    }
  );

• allow for "updating" config with an updater .update(current => { /* */ }).

• allow for "deleting" the config .delete().

• automatically skip applying config when nothing has changed (so we don't need this logic in each component).

• Have event listeners for delete and changed.

Then usage would just be to initialize sub-components with one of these in the constructor.