Provide absolute URL resolution

[DrewCarlson]

Jsoup provides good methods for resolving relative URLs as absolute URLs, we should have the same functionality https://jsoup.org/cookbook/extracting-data/working-with-urls

node-html-parser and Lexbor do not appear to provide any similar APIs so it will have to be implemented internally.

I'm not sure if Jsoup supports it, but it would be ideal if src attributes supported the same functionality.