[red-knot] Add boundness and declaredness tests (#15453)
## Summary
This changeset adds new tests for public uses of symbols,
considering all possible declaredness and boundness states.
Note that this is a mere documentation of the current behavior. There is
still an [open ticket] questioning some of these choices (or unintential
behaviors).
## Test plan
Made sure that the respective test fails if I add the questionable case
again in `symbol_by_id`:
```rs
Symbol::Type(inferred_ty, Boundness::Bound) => {
Symbol::Type(inferred_ty, Boundness::Bound)
}
```
[open ticket]: https://github.com/astral-sh/ruff/issues/14297
