url: adding WHATWG URL support

Implements WHATWG URL support. Example:

```
var u = new url.URL('http://example.org');
```

Many, many other commits improving the implementation have been squashed
into this backport PR. They are not listed separately here for brevity.

Backport-PR-URL: https://github.com/nodejs/node/pull/17365
PR-URL: https://github.com/nodejs/node/pull/7448


Reviewed-By: Ilkka Myller <ilkka.myller@nodefield.com>