utils/customError: narrow type of name property

The name property is inherited from Error and has a type of string.
But our CustomError ensures that the name is restricted to the type
of T. This causes compiler errors, so we had to enable a babel plugin
to support it.

config/jest/babelTransform.js

@@ -16,7 +16,11 @@ const hasJsxRuntime = (() => {
 })();
 
 module.exports = babelJest.createTransformer({
-  plugins: ['@shopify/react-i18n/babel'],
+  plugins: [
+    ['@babel/plugin-transform-typescript', {
+      allowDeclareFields: true
+    }], 
+    '@shopify/react-i18n/babel'],
   presets: [
     [
       require.resolve('babel-preset-react-app'),

config/webpack.config.js

@@ -427,6 +427,9 @@ module.exports = function (webpackEnv) {
                 ],
                 
                 plugins: [
+                  [require.resolve('@babel/plugin-transform-typescript'), {
+                    allowDeclareFields: true
+                  }], 
                   require.resolve('@shopify/react-i18n/babel'),
                   isEnvDevelopment &&
                     shouldUseReactRefresh &&

src/utils/customError.ts

@@ -2,6 +2,8 @@
 // Copyright (c) 2022 The Pybricks Authors
 
 export class CustomError<T extends string> extends Error {
+    declare name: T;
+
     public constructor(name: T, message: string, cause?: Error) {
         super(message, { cause });
         this.name = name;