PoC: Rollup Plugin without Unplugin

[timfish]

I had this stashed and thought I may as well open a PR so this code doesn't die on my laptop!

Should we do this?

Personally I think we should migrate away from unplugin because:

• We don't really use Unplugin as it was intended anyway and already have custom code per bundler
• We only need three bundler plugin "formats" to support all bundlers. Rollup, webpack and esbuild
• We are limited by Unplugins decisions over Node/bundler version support. v3 drops cjs/Node v18/webpack v4 (feat!: drop node 18 support, drop CJS build unjs/unplugin#558)

This PR drops using Unplugin for Rollup and instead just exports a single Rollup plugin that handles everything. For Vite we can just re-export the Rollup plugin with an additional wrapper.

Downsides?

If we add support for hook filters (#749), we would actually want the transforms to be contained in their own plugins because they would each need different regex filters for the best performance.

[github-actions]

Semver Impact of This PR

⚪ None (no version bump detected)

📋 Changelog Preview

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New Features ✨

• (telemetry) Add bundler-major-version tag to webpack by chargome in #857

Other

• PoC: Rollup Plugin without Unplugin by timfish in #858

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