Help users discover forked packages

The null safety migration has highlighted that, as in any ecosystem, there are many packages that are no longer maintained. I don't generally think that's a problem because forking exists as a mechanism to let the ecosystem to route around inactive packages.

However, forks can be difficult to discover. I dimly recall that GitHub started showing forks in its UI many years ago in large part for this reason. Have we considered trying to surface this in pub.dev for packages that have been forked? That may help users pivot to more recent forks of packages that have gone dormant.

cc @eseidelGoogle