be able to pre-parse `npm` commands about npx

[zkat]

@gabrielcsapo this is almost certainly not something that makes sense to have in npx itself.

If you want to replicate npm's CLI parsing, you can do it using two things: yargs and npm-package-arg. You use yargs to figure out the npm command (taking into account all the --flags), and then use npm-package-arg on the install targets, which will give you an object with all the information you're looking for here.