[Android] Constructor injection for Interactors is disallowed

After completing tutorial 2, I attempted to improve the Dagger usage by using constructor injection where possible. I succeeded in making RootRouter, LoggedOutBuilder, and LoggedOutRouter constructor injected and was able to remove a few manually-written @Provides methods as a result.

Next, I wanted to convert RootInteractor to use constructor injection. This would allow me to remove its manual creation from RootBuilder and make its presenter member private and final. But it appears that several features in the tooling prevent me from trying this:

• First, it's explicitly disallowed by InteractorAnnotationVerifier: "Interactor cannot have custom constructors - all dependencies and setup should happen in the builder of $type"
• If I disable that check, I get compilation errors because the generated Test*Interactor expects a no-arg constructor. It looks like I could maybe rewrite InteractorTestGenerator to be more flexible, but then I'd be getting pretty deep into the tools without knowing the framework that well.

So: Why is constructor injection of interactors disallowed?

Start by reading InteractorAnnotationVerifier and InteractorTestGenerator, then inspect RootInteractor and RootBuilder as described in the issue. Determine why custom constructors are rejected and how generated Test*Interactor depends on a no-argument constructor; done means documenting the constraint or defining the required tooling changes.