Use proposed go/types API #2
Description
To support generics, modver duplicates some of the logic in go/types that is presently unexported. There are two proposals to export some of that logic:
- x/exp/typeparams: a new module with a transitional API for tools golang/go#50447
- proposal: go/types: export term/termlist logic golang/go#50963
When and if those proposals become adopted, modver should use those calls.