Distributed component registration

[dnut]

Currently the macros are based around the idea that your app describes all of its components in one place. Most other dependency injection frameworks don't need this. You just annotate your component somehow, and it gets picked up.

This approach can already be accomplished with app-frame if you implement the correct traits adjacent to your component declaration, instead of using the application! macro. It's just very verbose, and it's not documented as an option, so it's not likely to be a common approach.

A macro could be added to do the same thing, to make this an explicitly supported use case. However, this could lead to a lot of confusion if people expect the application macro to be the single explicit location where components are associated with an application.