This PR renames `SharedUrl` to `SharedUri` to better reflect its intent.

I'm still not entirely happy with this naming, as the file paths that we
can store in here are not _really_ URIs, as they are lacking a protocol.

I want to explore changing `SharedUri` / `SharedUrl` back to alway
storing a URL and treat local filepaths differently, as it seems we're
conflating two different concerns under the same umbrella, at the
moment.

Release Notes:

- N/A