Provide taped-package suggestion hints

[MarcelGarus]

If tape assist is running and users create a @TapeClass that has a field of an external type, i.e. Flutter's Color, encoding won't work without registering an AdapterFor<Color>. It would be amazing if instead of failing at runtime, we could see that an AdapterForColor is missing in the tape.dart, lookup the package of the type (package:flutter), check if a taped_flutter package exists on pub.dev, and suggest that to the user.

[MarcelGarus]

The same should happen during adapter generation. Or should it only happen during adapter generation since the UX of notifying developers from a CLI tool that's running in the background is difficult?

[MarcelGarus]

As soon as you add @TapeClass to a class that contains a Color, maybe we should just add a comment to the field in question?
// TODO(tape): No adapter for Color registered. There's a flutter_taped package available that will solve this.
Of course, we should also remove such comments if the flutter_taped package is added.

[MarcelGarus]

For security reasons, we should also probably only suggest those packages that are registered in the table of type ids – otherwise, users could just upload something_taped packages for popular libraries to make us suggest them.