fix: re-add cjs outputs for v4 integration

[johnjenkins]

Pull request checklist

Please check if your PR fulfills the following requirements:

• Docs have been reviewed and added / updated if needed (for bug fixes / features)
• Build (pnpm run build) was run locally and any changes were pushed
• Tests (pnpm test) were run locally and passed
• Prettier (pnpm run prettier) was run locally and passed

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

GitHub Issue Number: Although stencil.config.ts looks like an ESM module, behind the scenes it resolves to CJS modules (and module imports).

The most recent version of stencil sass prematurely removed cjs output from the distributed package in preparation for stencil/core v5, forgetting that CJS is still required for v4. No integration tests are in the codebase meaning the regression was not picked up.

What is the new behavior?

• CJS modules are output again (via rollup config)
• A v4 integration test has been added to CI to prevent regression

Does this introduce a breaking change?

• Yes
• No

Testing

Other information