[display] report "abstractions" and "aliases" in statistics

Related to #9098. Statistics could report two additional kinds of relations for types:

- `aliases` - with `typedef A = B`, `B` has `A` as an alias
- `abstractions` - with `abstract A(B)`, `B` has `A` as an "abstraction"

In the UI we might choose to display these combined with subclasses / subinterfaces in a single "subtypes" code lense, but it would still be nice if the display response was this detailed for increased flexibility if we ever want to change the presentation or use the data or something else.