Fragments in URLs to project files cause 404s

This is a common need with the SVG `` element which needs a URL and a fragment to identify an element by id.

Here's a repro with a `` tag: https://lit.dev/playground/#gist=f5b3171f6cb1d37459832b9cae6193f3

Looking at the Network tab in dev tools, it doesn't look like the request URL includes the fragment, so I'm not sure if/how the service worker gets access to it, but it may need to strip of fragments before looking a file up in the project.