Firefox asks the cookies actor for rows after selecting a Storage host.
Read the browser cookie jar through the DevTools delegate and serialize
matching cookies with the fields Firefox expects.
This keeps mutation support disabled, but makes existing cookies visible
in the Storage panel.
Firefox discovers Storage panel data through watcher resources. This
adds a read-only cookies actor with the fields and empty store response
expected by the Storage panel.
Mutation traits are reported as unsupported for now.
DevTools storage resources all have a "host" key derived from the URL,
which we produce in `storage_host_for_url()`.