add Polyfill

I want to add Polyfill to new syntax such as Object.assign when packaging, for example, add useBuiltIns:'entry' to the corresponding babel configuration. What should I do, create a new babel configuration file, if so, what is the default babel configuration of the microbundle? I can modify it based on this

Start by locating Microbundle's packaging and Babel configuration entry points; the issue does not name a file or test. Read the existing default configuration and determine how polyfills such as Object.assign should be handled. Done means the supported configuration and expected polyfill behavior are clearly defined and covered by the relevant build checks.

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