fix incorrect refresh request when basePath is set (#64589)
`initialCanonicalUrl` differs from the `canonicalUrl` that gets set on
the client, such as when there's a basePath set.
This hoists the `canonicalUrl` construction up so we can re-use it when
adding refetch markers to the tree.
This also renames `pathname` -> `path` since it also includes search
params. I added a test to confirm no extra erroneous fetches happened in
both cases.
Fixes #64584
Closes NEXT-3130
