test: respect commonjs options in playgrounds

[patak-dev]

Description

Avoid forcing deps optimization for playgrounds that define custom commonjsOptions. When running pnpm run test-build-without-plugin-commonjs, this test: playground/external/__tests__/external.spec.ts was failing and is working now after the PR.

Note: in case you run the tests, we have another test in main failing with this env flag in playground/ssr-resolve that is unrelated to this issue.

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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[sapphi-red]

To make the external playground work with build dep-optimization, it seems we need to add a option to declare whether an external dependency is CJS or ESM.

[patak-dev]

I wonder if we could tell people to continue using the commonjs plugin for these deps in that case, so we try to avoid this cjs compat features if possible.