fix(legacy): skip esbuild transform for systemjs

[bluwy]

Description

fix #9618

The gist of the issue is that the esbuild plugin is used to built the polyfill chunk which includes the systemjs code. This PR skips esbuild for it.

Additional context

I think there are many ways to tackle this, so happy to discuss the best option here. e.g. should we always avoid esbuild for polyfill chunks?

I think this may invalidate #9453 too.

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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• Read the Contributing Guidelines.
• Read the Pull Request Guidelines and follow the Commit Convention.
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[sapphi-red]

#8660 is causing this issue.
My opinion here is to set optimizeDeps.esbuildOptions.target = 'es5' and esbuild = false.

#8660 set build.target = 'es5' to prevent esbuild to inject es2015 code when Esbuild Deps Optimization at Build Time is enabled. We could have the same affect with optimizeDeps.esbuildOptions.target.

[patak-dev]

This looks good to me as a hot patch, we can later review doing it in other cases too. Merging and running vite-ecosystem-ci, let's release vite and plugin-legacy

[patak-dev]

@sapphi-red saw your message after writing mine, we can do another release later with a better method if you want to do that PR.

[sapphi-red]

The difficult point is, when bundling a code with esbuild:

• if target is not es5, the code will transpiled to es2015+
• if target is es5, the code cannot include es2015+ code

Most code won't have any problem with transpiling es5 --(esbuild)--> es2015 --(babel)--> es5.
But for polyfill chunks, this seems sometime causes problems.

[sapphi-red]

should we always avoid esbuild for polyfill chunks?

I'm not sure about this. To be safe, maybe we should use terser with these options?
https://github.com/zloirock/core-js/blob/bac1385ec346896d4f0478a125817c47a5bea2a4/scripts/bundle.mjs#L1-L41