refactor(css): update CSS Modules to use CSS Layers

[joshblack]

Part of: https://github.com/github/primer/issues/6275

Update our *.module.css files to be in a CSS Layer following this ADR

Changelog

New

• Add test for CSS Layers to make sure that layers exist in CSS Module files and their naming matches our conventions outlined in the ADR

Changed

• Most CSS Module files are now wrapped in a CSS Layer

Removed

Rollout strategy

• [x] Minor release

This work will need to be rolled out alongside a change in github-ui where we remove the existing primer-react CSS Layer and use our layers instead.

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: 44dbc1028c72533e40351844614ef6a2bd517d25

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@primer/react	Minor

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[github-actions[bot]]

:wave: Hi, this pull request contains changes to the source code that github/github-ui depends on. If you are GitHub staff, test these changes with github/github-ui using the integration workflow. Or, apply the integration-tests: skipped manually label to skip these checks.