Allow specifying Dart Sass implementation

Created by: christopher-francisco

Description

For cases where you're not able to completely remove node-sass, causing sass-loader to pick it up, you can now explicitly specify you want to use Dart Sass through USE_DART_SASS=true env variable. See #9628 for the complete use case

Testing strategy

Manually tested it by doing the following

1. Created a new app with yarn create-react-app my-app
2. Added a few sass files with @use directive (only supported by Dart Sass)
3. Added sass dependnecy
4. Ran yarn start. Comiplation succeeded
5. Added node-sass dependency (we now have both)
6. Ran yarn start. Compilation failed
7. Ran USE_DART_SASS=true yarn start. Comiplation succeeded

Screenshot

You can see both sass and node-sass installed at the bottom right corner. App started with USE_DART_SASS=true yarn start

What's Missing?

• Find a way to automate a test similar to the one described above
• Updating documentation

Closes #9629