Since h has very liberal URI parsing compared to the browser's URL
constructor, as well as some completely invalid data on old annotations,
the client needs to handle errors parsing annotation `uri` values.

Surprisingly `annotation-metadata.js` is the only place I found in the
client that attempts to do this, everywhere else is just using the `uri`
field as a string.

Fixes https://github.com/hypothesis/client/issues/3666