Web specs do not return through javascript percent decoded URL path
components - but we were doing this in a number of places due to the
default behaviour of URL::serialize_path.
Since percent encoded URL paths may not contain valid UTF-8 - this was
resulting in us crashing in these places.
For example - on an HTMLAnchorElement when retrieving the pathname for
the URL of:
http://ladybird.org/foo%C2%91%91
To fix this make the URL class only return the percent encoded
serialized path, matching the URL spec. When the decoded path is
required instead explicitly call URL::percent_decode.
This fixes a crash running WPT URL tests for the anchor element on:
https://wpt.live/url/a-element.html
cc55732332