## Summary
This PR is a first step toward adding a GitLab output format to ty. It
converts the `GitlabEmitter` from `ruff_linter` to a `GitlabRenderer` in
`ruff_db` and updates its implementation to handle non-Ruff files and
diagnostics without primary spans. I tried to break up the changes here
so that they're easy to review commit-by-commit, or at least in groups
of commits:
- [preparatory changes in-place in `ruff_linter` and a `ruff_db`
skeleton](0761b73a61)
- [moving the code over with no implementation changes mixed
in](0761b73a61..8f909ea0bb)
- [tidying up the code now in
`ruff_db`](9f047c4f9f..e5e217fcd6)
This wasn't strictly necessary, but I also added some `Serialize`
structs instead of calling `json!` to make it a little clearer that we
weren't modifying the schema (e4c4bee35d).
I plan to follow this up with a separate PR exposing this output format
in the ty CLI, which should be quite straightforward.
## Test Plan
Existing tests, especially the two that show up in the diff as renamed
nearly without changes
1ce65714c0