feat: expose original request on WretchError

[dirkluijk]

Closes #264

[elbywan]

@dirkluijk Thanks a lot for the PR, and I'm sorry that I did not have time to review it earlier 🙇

The code looks good to me, the only issue is with node 14-16 / Request compatibility.

I am planning to release a new major version in a near future removing the burden of having all these legacy polyfills, but in the meantime how about setting the url/options as properties of the error instead of the request itself and let the consumer instantiate it?

Something like:

// Instead of setting the request
// err.request = new Request(finalUrl, finalRequestInit)
err.options = finalRequestInit

// (...)

try {
  // ... //
} catch (e) {
  console.log(e.response.url, e.options);
  const request = new Request(e.url, e.options);      
}

[elbywan]

The current major version of wretch is compatible with node v14, so using Request without polyfill would break the contract.