feat(ios, android) send epub positions data

[alecdhansen]

I found it useful to have access to the epub's positions data for building scrub control components, etc.

[jspizziri]

@alecdhansen why is the viewScope being used here?

[alecdhansen]

positions() and positionsByReadingOrder() are suspend functions, so I'm calling them inside a coroutine. By using this scope, everything cancels automatically if the View is destroyed, which should avoid leaks or unnecessary work.

Happy to hear your thoughts if something else would work better!

[jspizziri]

@alecdhansen , thanks for the PRs!

After taking a look at them, I'm now wondering if all the metadata events should be combined into a single one likeonPublicationReady which would contain the ToC, Positions, and Metadata. Since they're all available at the same time I'm not sure if splitting them out into separate events provides much benefit.

Interested in your thoughts.

[alecdhansen]

@jspizziri that makes sense to me. Your call! I could close these two PRs and open another one to combine the 3.

[jspizziri]

@alecdhansen That'd be great, thanks! We'll flag the ToC event as deprecated.