refactor(test-harness): remove parseDefaultValue and CEM-related logic from SSR renderer

[radium-v]

Pull Request

📖 Description

Remove the parseDefaultValue function and all Custom Elements Manifest (CEM) loading logic from the SSR renderer in @microsoft/fast-test-harness. This code was a workaround to populate default component state from CEM metadata during SSR test rendering, but it is no longer needed. State is now supplied directly through the test fixtures.

This is a refactor that reduces complexity and removes an implicit dependency on custom-elements.json files at render time.

📑 Test Plan

All existing tests pass. The parseDefaultValue test suite was removed along with the function itself. Remaining SSR renderer tests (renderTemplate, buildEntryHtml, buildState, createSSRRenderer) are unaffected.

✅ Checklist

General

• I have included a change request file using $ npm run change
• I have tested my changes.
• I have updated the project documentation to reflect my changes.
• I have read the CONTRIBUTING documentation and followed the standards for this project.