fs: more realpath*() optimizations

Including:

* Skip URL instance check for common (string) cases

* Avoid regexp on non-Windows platforms when parsing the root of a path

* Skip call to `getOptions()` in common case where no `options` is passed

* Avoid `hasOwnProperty()`

PR-URL: https://github.com/nodejs/node/pull/11665


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>