🐛 Bug Report

#3394 added a reference to ../../utils/useThemeConfig. That's fine if components are in @docusaurus/theme-classic, but if you swizzle a component you cannot reference that module.

Have you read the Contributing Guidelines on issues?

Yes

To Reproduce

$ npx @docusaurus/init@next init my-website classic
$ cd my-website
$ npx docusaurus swizzle @docusaurus/theme-classic Footer
Success! Copied @docusaurus/theme-classic Footer to src/theme/Footer.
$ npm run start
Module not found: Can't resolve '../../utils/useThemeConfig' in '/Users/treece/Desktop/my-website/src/theme/Footer'

Expected behavior

I'd expect the website to start, with a swizzled Footer

Actual Behavior

Site fails to start; Module not found: Can't resolve '../../utils/useThemeConfig' in '/Users/treece/Desktop/my-website/src/theme/Footer'

Your Environment

• Docusaurus version used: 2.0.0-alpha.66
• Environment name and version: Nodejs v12.16.2
• Operating system and version (desktop or mobile): MacOS