Include documentation in `index.d.ts`

[RunDevelopment]

I noticed that index.d.ts doesn't include any documentation even though a lot of useful comments are defined in the source files. Having inline documentation in your IDE of choice is very useful, so could it please be added in the next release?

The only thing that has to changed for this is the removeComments definition. This means that comments will also be included in the JS files, but that shouldn't be an issue since they aren't minified anyway.

Should I make a PR?

[MichaelDeBoey]

For people watching this issue: we've already started with our own fork in order to not hold the wider community back anymore: https://github.com/eslint-community/regexpp

@mysticatea We would still love to move the original repo to the new @eslint-community though.

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This PR is released in @eslint-community/regexpp v4.5.0
https://github.com/eslint-community/regexpp/releases/tag/v4.5.0