feat(plugin-react): make reactCompilerPreset work with @rolldown/plugin-babel's parallel option - #1549

Description

fixes #1547

reactCompilerPreset() set preset to an inline function. @rolldown/plugin-babel sends the Babel options to worker threads when parallel is set, and a function can't be structured-cloned, so babel({ parallel: true, presets: [reactCompilerPreset()] }) failed with "presets[0]" cannot be sent to a worker thread.

The preset is now a small module, dist/reactCompilerBabelPreset.js (a second tsdown entry). reactCompilerPreset() refers to it by path: preset: [babelPresetPath, options]. The module still resolves babel-plugin-react-compiler with import.meta.resolve from inside @vitejs/plugin-react, the same as before (#1270). The rolldown part (filter, applyToEnvironmentHook, optimizeDeps) stays on the main thread and is unchanged. Without parallel, Babel just loads the preset from the path, so the output is the same.

If the compiler options contain functions (e.g. logger), parallel still can't send them to a worker and @rolldown/plugin-babel reports the same error. Without parallel, these options keep working.

Tests

• New unit tests in reactCompilerPreset.test.ts: the preset survives structuredClone, and the referenced module adds babel-plugin-react-compiler with the given options. Both fail without this change.
• pnpm --filter @vitejs/plugin-react test-unit: 58 passed. pnpm lint and pnpm typecheck pass.
• pnpm test-serve compiler / pnpm test-build compiler pass.
• I also checked by hand with parallel: true set in playground/compiler and playground/compiler-react-18 (not committed). Before the change, vite build fails with the error from the issue. After it, the build works, the output contains the compiler's memo cache code, and the serve/build e2e tests for both playgrounds pass.

I wrote this with help from an AI assistant. I reviewed the change and ran the tests above myself.