fix(plugin-legacy): prevent esbuild injecting arrow function (fixes #8651)

[sapphi-red]

Description

Previously core-js was bundled by @rollup/plugin-commonjs but now it is bundled by esbuild.
esbuild injects helper functions and it uses ES2015 features when target is above ES5.

fixes #8651

Additional context

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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