Rollup merge of #121382 - nnethercote:rework-untranslatable_diagnostic-lint, r=davidtwco

Rework `untranslatable_diagnostic` lint

Currently it only checks calls to functions marked with `#[rustc_lint_diagnostics]`. This PR changes it to check calls to any function with an `impl Into<{D,Subd}iagnosticMessage>` parameter. This greatly improves its coverage and doesn't rely on people remembering to add `#[rustc_lint_diagnostics]`. It also lets us add `#[rustc_lint_diagnostics]` to a number of functions that don't have an `impl Into<{D,Subd}iagnosticMessage>`, such as `Diag::span`.

r? ``@davidtwco``

compiler/rustc_expand/src/base.rs

@@ -1493,6 +1493,8 @@ fn pretty_printing_compatibility_hack(item: &Item, sess: &Session) -> bool {
                             };
 
                             if crate_matches {
+                                // FIXME: make this translatable
+                                #[allow(rustc::untranslatable_diagnostic)]
                                 sess.psess.buffer_lint_with_diagnostic(
                                         PROC_MACRO_BACK_COMPAT,
                                         item.ident.span,