use urlpattern instead of path-to-regex for registry completions

[crowlKats]

Currently we use a custom implementation of path-to-regex just for registry completions; ideally we'd use the rust-urlpattern crate instead by exposing some of its internal methods. However, a blocker for this is whatwg/urlpattern#73, and also the fact that this change would be breaking, but releasing a v3 currently would make very little sense, as a v2 was released fairly recently and only deno.land has upgraded, whereas crux.land & nest.land still use v1.