[Bug] Legal comments is missing for files that are generated by esbuild splitting feature

**Describe the bug**
By default. esbuild output `legal comments` at the end of minified file.
https://esbuild.github.io/api/#legal-comments

For normal scripts/css files. It works as expected.
https://github.com/dotnet/docfx/blob/gh-pages/public/docfx.min.js#L71-L100

But some files generated by [esbuild splitting feature](https://esbuild.github.io/api/#splitting)
don't contains `legal-comments`. and restored source code from `.map` file also don't contains these comments.
https://github.com/dotnet/docfx/blob/gh-pages/public/es-ADFHJCQH.min.js

**To Reproduce**
Check [docfx site](https://dotnet.github.io/docfx) with browser's developer tools

**Expected behavior**
It can confirm third-party code license from distributed file.