refactor common test helpers into test/

This way we can share them with multiple tests

src/components/button.test.ts

@@ -1,7 +1,7 @@
 // SPDX-License-Identifier: MIT
 // Copyright (c) 2020 The Pybricks Authors
 
-import { lookup } from '../utils';
+import { lookup } from '../../test';
 import { TooltipId } from './button';
 import en from './button.en.json';
 

src/components/editor.test.ts

@@ -1,7 +1,7 @@
 // SPDX-License-Identifier: MIT
 // Copyright (c) 2020 The Pybricks Authors
 
-import { lookup } from '../utils';
+import { lookup } from '../../test';
 import { EditorStringId } from './editor';
 import en from './editor.en.json';
 

src/components/notification.test.ts

@@ -1,8 +1,8 @@
 // SPDX-License-Identifier: MIT
 // Copyright (c) 2020 The Pybricks Authors
 
+import { lookup } from '../../test';
 import { MessageId } from '../reducers/notification';
-import { lookup } from '../utils';
 import en from './notification.en.json';
 
 describe('Ensure .json file has matches for MessageIds', () => {