feat(metro-config): add sass (#22031)

# Why

Standard feature for modern web support.

# How

- When a project has CSS setup and `sass` installed, they can use sass
syntax in scss/sass files.

feat(metro-config): add sass (#22031)

# Why

Standard feature for modern web support.

# How

- When a project has CSS setup and `sass` installed, they can use sass
syntax in scss/sass files.
- Sass is compiled to CSS before it's passed to the standard CSS
handling. This means that css modules also support sass.
- Just like standard CSS support, importing external files is not
currently supported.

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# Test Plan

- tbd

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# Checklist

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- [ ] Documentation is up to date to reflect these changes (eg:
https://docs.expo.dev and README.md).
- [ ] Conforms with the [Documentation Writing Style
Guide](https://github.com/expo/expo/blob/main/guides/Expo%20Documentation%20Writing%20Style%20Guide.md)
- [ ] This diff will work correctly for `expo prebuild` & EAS Build (eg:
updated a module plugin).

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Co-authored-by: Expo Bot <[email protected]>

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