Implement a way to list all features of all dependent packages

in another thread, `cargo read-manifest` followed by parsing the JSON yourself was suggested. I'd be ok doing that, but it also doesn't seem to work. No features are listed in each create in the json, from what i can see.

Start by reproducing the reported `cargo read-manifest` output and inspect how its JSON represents dependency packages and features. Determine the command or entry point that should expose this information; done means users can list all features for every dependent package, with the behavior verified against the reported manifest case.

Written by the indexing model from the issue text.