Rollup merge of #108482 - Ezrashaw:force-error-docs, r=GuillaumeGomez

statically guarantee that current error codes are documented

Closes #61137 (that's right!)

Pretty simple refactor (often just a change from `Result<Option<&str>>` to `Result<&str>`)

r? `@GuillaumeGomez` (could you specially look at 53044158eff0d64673a6100f701c57b484232aca? I believe you wrote that in the first place, just want to make sure you're happy with the change)

compiler/rustc_errors/src/lib.rs

@@ -1477,9 +1477,7 @@ impl HandlerInner {
                 .emitted_diagnostic_codes
                 .iter()
                 .filter_map(|x| match &x {
-                    DiagnosticId::Error(s)
-                        if registry.try_find_description(s).map_or(false, |o| o.is_some()) =>
-                    {
+                    DiagnosticId::Error(s) if registry.try_find_description(s).is_ok() => {
                         Some(s.clone())
                     }
                     _ => None,