Merge #4273

4273: Trigger add_vis assist on paths/record fields as well r=flodiebold a=TimoFreiberg

Resolves #4037.

- [x] Function defs
- [x] ADT defs
- [x] Enum variants
- [x] Consts
- [x] Statics
- [x] Traits
- [x] Type aliases
- [x] Modules
- [x] Record fields (using different implementation)
    - [x] struct fields
    - [x] enum variant fields
    - ❌  union fields (`Semantics::resolve_record_field` seems to not work for union fields, so I think this can be handled in a future PR)
- [x] More tests? 
- [x] Improve test fixture code and documentation a bit (see [Zulip](https://rust-lang.zulipchat.com/#narrow/stream/185405-t-compiler.2Fwg-rls-2.2E0/topic/resolve_path.20between.20fixture.20files))

Co-authored-by: Timo Freiberg <[email protected]>

Author: bors[bot]