lint: add diagnostic translation migration lints

Introduce allow-by-default lints for checking whether diagnostics are
written in `SessionDiagnostic`/`AddSubdiagnostic` impls and whether
diagnostics are translatable. These lints can be denied for modules once
they are fully migrated to impls and translation.

Signed-off-by: David Wood <david.wood@huawei.com>

compiler/rustc_lint/src/lib.rs

@@ -508,6 +508,8 @@ fn register_internals(store: &mut LintStore) {
     store.register_late_pass(|| Box::new(ExistingDocKeyword));
     store.register_lints(&TyTyKind::get_lints());
     store.register_late_pass(|| Box::new(TyTyKind));
+    store.register_lints(&Diagnostics::get_lints());
+    store.register_late_pass(|| Box::new(Diagnostics));
     store.register_lints(&PassByValue::get_lints());
     store.register_late_pass(|| Box::new(PassByValue));
     store.register_group(