Split ColorConfig off of HumanReadableErrorType

The previous setup tied two unrelated things together. Splitting these two is a better model.

compiler/rustc_interface/src/tests.rs

@@ -315,7 +315,8 @@ fn test_search_paths_tracking_hash_different_order() {
     let early_dcx = EarlyDiagCtxt::new(JSON);
     const JSON: ErrorOutputType = ErrorOutputType::Json {
         pretty: false,
-        json_rendered: HumanReadableErrorType::Default(ColorConfig::Never),
+        json_rendered: HumanReadableErrorType::Default,
+        color_config: ColorConfig::Never,
     };
 
     let push = |opts: &mut Options, search_path| {