Test: Use native Vite transforms for unit tests

[ciampo]

Part of #80855.

What?

TL;DR — transform changes: replace the private Babel-wide Vitest transform with Vite's official React/SWC path, remove the Jest-only block metadata transformer, and migrate the remaining internal agent-tool test to Vitest.

Why?

The final runner should use native Vite module handling rather than carry the legacy Jest/Babel execution pipeline into Vitest.

How?

• Use @vitejs/plugin-react-swc with the official Emotion SWC plugin.
• Preserve readable Emotion labels and normalize generated hashes only in diff snapshots.
• Replace Babel parsing in the conventions validator with typescript-eslint.
• Migrate tools/agents tests to explicit Vitest imports.
• Replace the Jest cache-key transformer with a Vite module-graph test proving block.json invalidation.
• Remove the unit workspace's direct Babel transform dependencies.

Runtime requirements

@vitejs/plugin-react-swc@4.3.2 requires Node ^20.19.0 || >=22.12.0, matching Gutenberg's existing Node floor. The npm minimum remains >=10.2.3.

Testing Instructions

1. Run npm run test:unit:routing and npm run test:unit:conventions.
2. Run the Node project, all four jsdom shards, and the Browser project.
3. Run npm run test:unit -- --runInBand.
4. Run focused lint for test/unit and tools/agents.

Testing Instructions for Keyboard

Not applicable; this changes test infrastructure only.

Use of AI Tools

Codex assisted with implementation, compatibility checks, and verification. The resulting changes and snapshots were reviewed by the author.

[github-actions]

Size Change: 0 B

Total Size: 7.76 MB

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[github-actions]

Flaky tests detected in ccc5142.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/30598125515
📝 Reported issues:

• [Flaky Test] should paginate, navigate pages, and diff across page boundaries #80154 in /test/e2e/specs/editor/various/revisions.spec.js