Improve TypeScript declaration of @turf/points-within-polygon

[rugheid]

Please fill in this template.

• Use a meaningful title for the pull request. Include the name of the package modified.
• Have read How To Contribute.
• Run npm test at the sub modules where changes have occurred.
  The tests crash with me locally, but I tried linking the package to the project I'm working on and the types work.
• Run npm run lint to ensure code style at the turf module level.
  Lint also doesn't work for me locally, but it should be ok I guess.

This PR improves the TypeScript declaration for points-within-polygon to make sure the output points contain the same GeoJSON properties as the input points.

[mfedderly]

Thanks!