Extracted out of https://github.com/denoland/deno/pull/27838/files
Reduces some allocations by accepting either a pathbuf or url for the
referrer for resolution and returning either a pathbuf or url at the
end, which the caller can then convert into to their preferred state.
This is about 4% faster when still converting the final result to a url
and 6% faster when keeping the result as a path in a benchmark I ran.
