Combine lint and syntax error handling (#18471)
## Summary
This is a spin-off from
https://github.com/astral-sh/ruff/pull/18447#discussion_r2125844669 to
avoid using `Message::noqa_code` to differentiate between lints and
syntax errors. I went through all of the calls on `main` and on the
branch from #18447, and the instance in `ruff_server` noted in the
linked comment was actually the primary place where this was being done.
Other calls to `noqa_code` are typically some variation of
`message.noqa_code().map_or(String::new, format!(...))`, with the major
exception of the gitlab output format:
https://github.com/astral-sh/ruff/blob/a120610b5b01a9e7bb91740a23f6c2b5bbcd4b5f/crates/ruff_linter/src/message/gitlab.rs#L93-L105
which obviously assumes that `None` means syntax error. A simple fix
here would be to use `message.name()` for `check_name` instead of the
noqa code, but I'm not sure how breaking that would be. This could just
be:
```rust
let description = message.body();
let description = description.strip_prefix("SyntaxError: ").unwrap_or(description).to_string();
let check_name = message.name();
```
In that case. This sounds reasonable based on the [Code Quality report
format](https://docs.gitlab.com/ci/testing/code_quality/#code-quality-report-format)
docs:
> | Name | Type | Description|
> |-----|-----|----|
> |`check_name` | String | A unique name representing the check, or
rule, associated with this violation. |
## Test Plan
Existing tests
