Automatically detect and either warn or follow un-exported dependencies

[demsullivan]

If you export a type and it depends on other types that are not exported, it would be really handy if dry-typescript could warn the user about this, or even automatically follow the dependency. For example

module Types
  include Dry.Types()
end

module A
  User = Types::Hash.schema(id: Types::String, name: Types::String)
end

module B
  extend Dry::Typescript
  ts_export Users = Types::Array.of(A::User)
end  

In this example, dry-typescript would export:

export type Users = Array<{ id: string, name: string }>

Ideally, it should either flag that Users references a type from another unexported module, or it should follow the dependency automatically, and output:

export type User = {
  id: string;
  name: string;
}

export type Users = Array<User>;

The current solution for this would be to use ts_export_all to export A:

module B
  extend Dry::Typescript
  ts_export_all A
  ts_export Users = Types::Array.of(A::User)

However, it would be a much better user experience if we could at least warn the user about this situation, so we can suggest to them that they export the dependencies.

[demsullivan]

@robyurkowski