analyze: generate subset relationships for arguments such as arg: &'a &'b &'c i32

[aneksteind]

The 'c: 'a bound that's implied by well-formedness of arg's type should definitely show up somewhere. I think I've seen bounds like that in the output of either predicates_of or a related query. Maybe try looking at explicit_predicates_of, inferred_outlives_of, and/or predicates_defined_on.

It would also be fine to just leave a comment about the limitation, especially if you can't find an easy way to get the predicate from rustc.

Originally posted by @spernsteiner in #975 (comment)

A FIXME comment was added in 3a50eec8