Rename `errors.rs` file to `diagnostics.rs` (1/N) `errors.rs` (and sometimes `error.rs`, depends on the crate) are not coherent with their content which can be both errors and lints. However, they're both diagnostics so it would make more sense to rename all of them into `diagnostics.rs`. I only did 3 crates for a start to confirm it's ok to go forward with this. I think it was discussed with @JonathanBrouwer so setting them as reviewer. :3 r? @JonathanBrouwer