Rollup merge of #98884 - davidtwco:translation-on-lints-derive, r=oli-obk

macros: `LintDiagnostic` derive

- Move `LintDiagnosticBuilder` into `rustc_errors` so that a diagnostic derive can refer to it.
- Introduce a `DecorateLint` trait, which is equivalent to `SessionDiagnostic` or `AddToDiagnostic` but for lints. Necessary without making more changes to the lint infrastructure as `DecorateLint` takes a `LintDiagnosticBuilder` and re-uses all of the existing logic for determining what type of diagnostic a lint should be emitted as (e.g. error/warning).
- Various refactorings of the diagnostic derive machinery (extracting `build_field_mapping` helper and moving `sess` field out of the `DiagnosticDeriveBuilder`).
- Introduce a `LintDiagnostic` derive macro that works almost exactly like the `SessionDiagnostic` derive macro  except that it derives a `DecorateLint` implementation instead. A new derive is necessary for this because `SessionDiagnostic` is intended for when the generated code creates the diagnostic. `AddToDiagnostic` could have been used but it would have required more changes to the lint machinery.

~~At time of opening this pull request, ignore all of the commits from #98624, it's just the last few commits that are new.~~

r? `@oli-obk`

compiler/rustc_macros/src/lib.rs

@@ -129,6 +129,7 @@ decl_derive!(
         // struct attributes
         warning,
         error,
+        lint,
         note,
         help,
         // field attributes
@@ -141,6 +142,24 @@ decl_derive!(
         suggestion_hidden,
         suggestion_verbose)] => diagnostics::session_diagnostic_derive
 );
+decl_derive!(
+    [LintDiagnostic, attributes(
+        // struct attributes
+        warning,
+        error,
+        lint,
+        note,
+        help,
+        // field attributes
+        skip_arg,
+        primary_span,
+        label,
+        subdiagnostic,
+        suggestion,
+        suggestion_short,
+        suggestion_hidden,
+        suggestion_verbose)] => diagnostics::lint_diagnostic_derive
+);
 decl_derive!(
     [SessionSubdiagnostic, attributes(
         // struct/variant attributes