Handle expansion of complex transitive reactive hints

[stephenh]

Given a non-persisted async property like Book.owner:

class Book {
  readonly owner: AsyncProperty<Book, Author | Publisher> = hasReactiveAsyncProperty(
    { author: ..., publisher: {} },
    return ...business logic choses either author or publisher...;
  });
}

And another reactive async property like Book.ownerName:

class Book {
  readonly ownerName: AsyncProperty<Book, string> = hasReactiveAsyncProperty(
    { owner: "name" },
    return owner.name;
  });
}

When a 3rd property wants to reactively depend on Book.ownerName, how do we expand the "owner" reactive hint into the correct reactive hint?

Specifically b/c owner's reactive hint may need the new "name" extension added to multiple places (for Author.name or Publisher.name) which may or may not be leaf properties in the hint.

Also, at runtime we only know that we need to add a "name" hint somewhere within the owner hint; we currently don't know that owner only returns Author | Publisher, to at least look for the subset of hint locations that match those entity types.

[stephenh]

Interesting example where both the ITIs returned from the variantsOfItem hint but also the "this" iti itself, both would need to be reactive:

  readonly variantsAndSelf: Collection<ItemTemplateItem, ItemTemplateItem> = hasManyDerived("variantsOfItem", {
    get: (iti) => [iti, ...iti.variantsOfItem.get],
  });