Include file extension for transformed workspace packages

[janpe]

Hi! I'm having an issue that is similar to #89.

I have a package in my repo that is not published, let's call it @myorg/mypkg and in my tsconfig I have a path for it like this:

"paths": {
      "@myorg/mypkg": ["./packages/mypkg/src/index.js"],
}

When I transform the paths with this configuration I end up without both the index filename and the .js extension, both of which I'd need preserved.

The end result in this case are paths like this:

export * from "../../mypkg/src/

[janpe]

Just stumbled upon #136 and it seems like it would resolve this problem